1. the post already said why:

I would love to move away from reddit but it's hard when this is where the base of my favorite communities still exists.

2. further compounded by issues such as (a) overall lack of moderation, which further depends on (b) better development of moderation tools, and (c) guides explaining how things work, bc it can be fairly confusing, e.g.:

How do I find selfhosted communities on Lemmy? If I search for "selfhosted" I get one community (Run It Yourself) with around 3K subscribers and very little activity. Is that it?

Though someone answered (I think incorrectly):

I think the biggest one is 40k on lemmy.world and it's called "selfhosted". You must be on a Lemmy server that doesn't show that community for some reason. There are ideological rifts on Lemmy that can cause some servers to splinter like that.

Interestingly, from my old instance discuss online, I see no hits at all to that term among community names - https://discuss.online/search?q=selfhosted&type=Communities&listingType=Local - meaning that nobody from that instance has subscribed to it yet.

Which is why things like Categories of Communities (already fully functional on PieFed) are so helpful to guide people to what they may be looking for.

3. And I haven't even begun on the whole tankies connotation of moving here.

I think it's clear-cut that the selfhosting community on Lemmy is a perfect alternative to reddit.

No - apparently not, it's only clear to you, not them, for all the reasons listed above and likely more besides. We would have to build it first, before they will come... and even then I would expect a long delay. In the meantime, Lemmy MAUs (Monthly Active Users) are actively declining, whether they are returning their traffic to Reddit or not.