On March 21, 2006 the first ever tweet was posted by Twitter founder Jack Dorsey: “Just setting up my twttr”. It was a simple introduction to a brand new platform.

Backed by celebrities, it was different to other social media sites, like MySpace or Facebook, because you could interact with any user without them having to approve a request. Companies rushed to join the service, hoping to get closer to their customers.

“If you were a brand that wanted to be part of any cultural moments that were happening, Twitter was a great place to be,” Alex Wilson, a senior strategist at the marketing agency Pitch tells BBC News.

On June 4, 2010 Elon Musk, the owner of Space X, logged on for the first time: “Please ignore prior tweets, as that was someone pretending to be me 🙂 This is actually me.”

Twelve years later he would buy the platform for $44bn (£38.1bn), reshape the algorithm, reinstate banned accounts, repurpose the policy around “free speech”, and rename it X.

He also fired thousands of staff – around 80% of the workforce.

Since Mr Musk’s takeover companies have been choosing to leave the platform in what’s been termed “the great X-odus”.

One of their main concerns was the content that would be seen around their posts that users could screengrab and share.

For example, between June 2022 and February 2023 antisemitic posts on X doubled, according to research by the Institute of Strategic Dialogue.

More recently in the UK, Mr Musk’s posts about British politics have stirred up controversy.

In particular, his posts on the subject of grooming gangs put pressure on the government, which announced a review of the issue.

“There is no doubt that Musk’s ownership of X is having an impact on public opinion in the UK,” Luke Tryl from the research group More In Common tells BBC News.

However, according to More In Common, only 16% of Brits believe his interventions are designed to achieve justice for victims, whereas 44% think he is doing it for attention, and his approval rating with the British public sits at -35.

The changing tone of X and the controversy surrounding its owner have spurred some firms to leave the platform and others have pulled their advertising as well.

At the end of 2023 firms including Apple, IBM and Disney paused advertisement on the platform.

Others brands including Unilever and Mars were sued by Mr Musk, who accused them of unlawfully agreeing to boycott the site.

“It’s broadly fair to say Twitter is becoming less relevant across the world,” Mr Wilson says in the Pitch office in central London, with posters of clients ranging from charities, telecommunications, and sports leagues.

“It’s been a very long time since clients came to us and say: ‘Twitter’s fun and exciting. We want to be in that space’.

“Unless you are targeting specific audiences, maybe certain political audiences or sports – football is still big on Twitter – it’s hard to see the value in it.”

Trump’s election victory has prompted other organisations to leave X, with others considering their positions as Mr Musk’s influence in the White House grows.

Beginning in 2013, German football team FC St Pauli, which plays in Germany’s top league, the Bundesliga, posted more than 60,000 times, racking up nearly 250,000 followers.

But less than 10 days after Trump’s return to the White House was confirmed, the club posted: “You can find our statement about saying goodbye to X on BlueSky. Feel free to follow us there. We’re out of here.”

“We discussed the decision for a year. We were mostly posting content with counter speech to hate. We had a lot of content for diversity, anti-racism, and anti-sexism,” club spokesperson, Patrick Gensing told the BBC.

“We have seen assaults on X, antisemitism, conspiracy theories,” he says.

The argument that such posts are justified by freedom of speech, does not convince him.

“We don’t think racism is freedom of speech,” says Mr Gensing.

One of the most recent departures from X was by the UK arm of BMW. In late January it announced it was no longer posting on X and directed people to its posts on Facebook and Instagram.

There’s no definitive way to know how many brands are choosing to leave or reduce their posts on the platform.

When approached, X did not respond to the points raised in this article. But last year Mr Musk claimed X had 600 million monthly active users, and said the platform maintains its “purpose is to serve the public conversation”.

Mr Musk “has been clear that X is willing to make trade-offs to adopt a more open, less moderated approach compared to Twitter”, says Goran Calic, visiting scholar at Harvard Business School.

But leaving X can have negative consequences for organisations and their relationships with customers.

“When users leave, the impact depends on who is leaving and why. A local authority posting news provides significant value to the network. If such an account leaves, it can hurt both the platform and its users,” he tells BBC News.

“Users protesting by leaving should weigh the broader social implications of staying versus exiting.”

For some organisations who need to get their message out quickly, X still has value that other competitors simply can’t offer.

“For us there is still that value [on being on X],” says Andrew Cassidy, senior director of digital strategy and engagement at the Massachusetts Bay Transportation Authority (MBTA).

“We try to match where our riders are. When people are tweeting at the MBTA someone can provide a definitive answer in the moment. Our broadcasting system is exclusively tied into our X account, but we still field customer service questions across other platforms.”

“Our focus is providing customer service to the largest number of riders that we possibly can,” Mr Cassidy says.

“With the current landscape being what it is, X still feeds that need.”

It’s “unthinkable”, Mr Gensing explains, not to have a presence on social media in 2025.

“We have to view all the platforms critically, it’s not only X. The companies behind them set up the rules of the game and they can change them.”