Twitter's bread and butter was always that it was a platform that was attractive to celebrities and politicians and have them a direct line of communication to their fans. The celebrity accounts then drew in a large userbase.

If there's one thing famous people doesn't want it is to get an uncensored feed of what people think of them. They want to have the sort of engagements that promotes the kind of personal brand they are building for themselves. If you're a big pop star you don't want to have people posting creepy sex stuff at you, if you're a queer icon you don't want a deluge of homophobia and if you're building a brand as a very serious politician you don't want a feed full of people explaining why your bullshit doesn't add up. The block function is a core feature to keep Twitter's most business-critical users on the platform. Removing it will be idiotic from a business perspective.