to be fair this isn't a particularly new issue, I suppose it's a lot more apparent now than ever but there have been numerous moments in the past where there's like only 2-3 maps at most in the qualified section compared to other modes that might have twice or triple the amount and more.
Why is this a issue? outside of the mode just simply not being that popular compared to the other modes I couldn't tell you. maps generally have to go through several stages before they can reach the ranked section. They must first get at least 5 hypes which is usually not that hard (can always ask a friend or request in mapping dicsord servers or certain modding queues) this is basically upvoting the map. Then there's having to receive Mods(feedback) which might be problematic given a large portion of modders are BNs in catch at least from what I've seen. Requesting to BNs can be a hit or miss at times especially if you don't have an established connection with them already since you REALLY have to take into consideration their preferences as well as maintaining a certain level of map quality which I'll get to that later.
Once you've received enough mods you need to get 2 BNs to do a check on your map for any mistakes/unrankables or suggestions. if all is good it is free to get nominated by the BNs where it now qualified until 7 days until it can get ranked unless an issue is spotted where it gets dq'ued until the isssue is resolved where it has to re-nominated by those or 2 other BNs
As a new mapper, this might be difficult to deal with and perhaps intimidating to an extent thus communication is crucial for any meaningful progress. Modding queues are one such way of at least getting some feedback on how you could improve but that's no good for catch since all the forums are pretty inactive (they're almost all closed or haven't been touched in years). you are may be left with the other option of using the chats #mapping and #modreq but good luck with that honestly. alright so that's 2 options down, what now? You could perhaps go to modding servers on discord which Is perhaps the single best and maybe only option to use if you want to take mapping seriously. There seems to still be a genuine community centred on mapping in catch but It's probably a bit small but It does exist.
So if I had to take a guess it's maybe a mix of fatigue from existing mappers/modders/BNs, not enough influx of new mappers, weird and ambiguous barrier of entry.