For me the main criteria is: if I want to get an answer to a question, especially a non trivial one which is not releated to lemmy/fediverse - I should better go to reddit.

You’re not wrong, but I don’t see why Lemmy would want to replicate reddit in that respect. You don’t need to spend any time on reddit or even make an account to take advantage of that functionality. You just Google your question and add reddit to the end and voila.

Probably, can you give me example of such communities which are not about fedeverse, technology, foss or memes?

I also skipped the gaming and political communities because there is an absolute boatload of that content on Lemmy, as I’m sure you’re aware. These are some communities that I am subscribed to that jumped out as being fairly active.