The difference is if the primary (sometimes only) admin of your instance loses interest, goes to jail, or gets hit by a truck, your entire instance could be dead in the water, whereas there are way more safeguards to “established” social media like Reddit and Twitter. Plus the issue of “well shit my instance got defederated from most of the fediverse because it turns out the admin is an asshat” is completely nonsensical on platforms without instances. Example: before I knew that Lemmy had a tankie problem, I almost signed up on lemmygrad because I thought it was just a witty pun…
Plus when you say “point them to lem.ee” what scenario are you imagining? Because “you should join reddit” or “our business is on Facebook” or “Twitter is a great resource for artists” are all straightforward and easy pieces of information to convey and pick up. “Join Lemmy, a subset of the fediverse, I signed up via lemmy.world although I hear lem.ee is also good, but don’t let that stop you from picking another instance” is like… Dude, people just want to go to [site].com, click on “sign up”, enter a username and password (and maybe email) and that’s it. Just having to explain to people that “lemmy.com” isn’t a thing is already too complicated for most folks.