It’s a little more than a slightly better UX. Dismissing the entire concept of the instance removes a fair amount of complexity and fragmentation from the equation. There are so many cheerful guides out there about how to select an instance and every single one of them loses 95% of normal people in the first paragraph.

Having a signup model that people understand helps. Concentrating everything in one schema creates a noticeable increase in density of relevant content. Having corporate money for real hosting and security counts. When you fediverse instance goes down to DDOS or implements crippling safeguards because they can’t keep up with the spam, you really feel how the whole thing is run on a shoestring.