This is not the first time that Twitter has blocked links to other platforms.
In 2018, Twitter blocked links to the Gab social network, which has been accused of hosting white supremacist content.
Twitter has also blocked links to other social media platforms, such as TikTok and Facebook. These blocks have been criticized by some as censorship. This suggests that Twitter is not afraid to use its power to stifle competition.
It is unclear why Twitter has blocked links to Threads.net. It is possible that Twitter is concerned about the spread of misinformation on Threads. It is also possible that Twitter is simply trying to protect its own traffic.