@hirad it's a little more complicated than that.
As one of the major #Fediverse players, it's more like Fediverse is the social network while #Mastodon is the interface or app to access it.
So one could say that Mastodon is a microblogging interface to a social network with diverse content.
How to bridge that gap is a constant question for any program interfacing with Fediverse: say you expand Mastodon to fully support longform content... then what happens when a video comes down the wire?
There's no single answer to that question, so if Mastodon wants to maintain strict focus on microblogging that makes sense. But it also makes sense to expand.
It's whatever the devs prefer.