Quintessentially, the way Mastodon.social is is because that's what the Mastodon devs want Mastodon to be. The ability to post with a "cut" for "read more" is an unofficial mod to the basic Mastodon server software.
That said, all Mastodon pods support storing these posts and showing them. The Mastodon devs aren't "forcing" their way on us all. We can choose a pod with that mod.
It's not always that simple, of course. The pod I wanted to move to... oh well I'm still working on it.