"I think it's probably doomed. It'll never overtake reddit. But, it'll be a nice, quiet, alternative."
No one knows if it is doomed.
You have to start somewhere but you can't expect a platform that has seen an huge influx of users the past weeks to immediately operate on the scale of what Reddit does.
"I humbly apologize for my personal, speculative, opinion about the unknowable future. The downvotes have made me realize my math was wrong, my opinion is wrong, and I am wrong. My corrected opinion is that Lemmy will overtake Meta, Mastadon, Twitter, and Google (wtf is reddit!?), and every upvote will be worth $1000, making everyone rich! Or, we can have fun guessing, and wait and see how things go. I hope they go well!"
Who is claiming the above?
The fun thing is that Mastodon is in your list and before the fuckery with Twitter it didn't really have traction.
Why can't lemmy/Kbin be the same in a year from now?
The problem for Reddit, is that it made people actually look for alternatives. It is stupid for a competitor to make it's customers aware of the competition, but Reddit did exactly that.
Maybe it flops, maybe it stays "niche", maybe it explodes in popularity.
I think it is indeed random chance and just being at the right place at the right time.