Kingdom design used to be a bigger discussion topic here back when certain tournaments featured submitted kingdom designs. It’s a lot of work, but could lead to some really cool boards. I could see such a tournament making a comeback at some point.
I agree with LF that the reason it’s rare is that random kingdoms are often pretty interesting these days. Dark Ages in particular has quite a bit more trashing, which is often the key ingredient making eng8nes possible. Second editions of Base and Intrigue also removed some of the biggest duds, meaning you interact with more of the kingdom.
That said, random kingdoms are never going to be as good as designed kingdoms, and I’d hope that designing would come back into the mix at some point. Personally, I would love to see more kingdoms where there are multiple reasonable strategies rather than one clearly dominant strategy both players aim for.
I always think in terms of tournaments, but I guess designing also happens in the Puzzles thread, e.g. the quest to find kingdoms where the first player can win on their first turn.
I guess that actually illustrates a problem with designed kingdoms in a tournament context these days: They can be just ridiculously nuts with certain events and some newer cards like Villa. Like Donate boards in general, this has the potential to make every kingdom into a puzzle, which is fun in small doses, but might be tiring to play repeatedly. I suppose this is just something for designers to keep in mind, though.