Plus the reality of the fediverse is if you want to use multiple platforms, you wind up needing multiple accounts anyway. Like if I want to upload to Peertube, I need to make a Peertube account, so we're back to where we started of having multiple places to follow people since I can't use my Mastodon account to upload to Peertube. I'm able to have some cross-platform interaction, like commenting on videos from mastodon - but there's issues there like, Pixelfed only showing people posts with images.
When talking to most people I just call the whole thing Mastodon and treat it like its a single app/service, because that's what people are used to. If I start trying to tout how the fediverse is a decentralized platform of multiple applications and you can kinda/sorta interact across platforms - people's eyes glaze right over. They just do not care.
For apps - I've never met a person that picks a messenger because its tweaked for their platform. They just prefer whatever their friends are on. iMessage is something of a odd case since Apple just rolls you into it automatically and presents it via the default app.