Monday, 20th May 2019, 12:22 by sanka
Developers can give you better reasons then me (or some other random posters here), but here I my answers anyway:
1. I do not think there is any reason behind some resistances being 3 levels and others only 1. Poison resistance is not very important even with 1 level, so 3 would be even more strange. Otherwise having only 1 level of every resistance had been proposed, and seems to be better from a game design standpoint, as otherwise you are encouraged to carry more rarely useful items to swap. (Although some people argues that removing resistances all together would be more sensible from a game design perspective.)
I think the 3 levels are mostly heritage. Resistances are not very important or a big part of crawl in any case, I guess nobody cares enough to rebalance them to something better.
2. I guess cure poison had been removed because it was mostly useless, and since poison status is not a big threat anyway there is no need to have even more ways to get rid of it and make it even more trivial.