It was probably due to pressure from the Ecuadorian government. They have imposed ridiculous censorship on Assange and his colleagues lately. Read more about that here.

They're basically threatening Assange with extradition to the US or UK if his friends and colleagues convey anything journalistic that Assange himself would publish.

Assange's Twitter account has been run by his legal defense team since the embassy cut him off from the internet and they have continued to publish what Ecuador would consider criticisms of Ecuador and its 'friendly' nations.

So I would not be surprised if the Ecuadorian government pressured Twitter to suspend the account