Switch local wireless is capped to 8 systems; devs can't use more if they wanted to. I don't recall where I've read that (and the hard proof is likely under NDA); however, if you want soft proof, the Shoal in Splatoon 2/3 is limited to 8 systems in local wireless while it supports 10 over LAN (8 players, 2 spectators). While 8 is likely a cautiously low limit, my guess is it wouldn't scale well to 35 systems, let alone 99; too much wireless traffic in the same space. Wireless bandwidth goes down fast as you increase devices, because devices cannot transmit at the same time.
These games don't support non-full matches as a design choice, so there's no reason to include a local wireless mode. You could in theory do LAN, but LAN is kind of an unspoken thing on the Switch; Nintendo even hides it in their menus. Yes, it'd be good for preservation, but the reality (on the Switch) is that devs don't value LAN if they're not already using local wireless, because almost no one takes advantage of LAN.
It's not a coincidence as much as it is common factors at play. For one, Nintendo has been averse to dedicated servers, only using them in games where P2P play is just not feasible due to player count - which is the same reason local wireless isn't feasible.
Third parties are less scared of dedicated servers, but they also just rarely implement local wireless in general, servers or not. But similarly, the need for servers goes up as player count does, so there's similar biases at play. There's nothing preventing an 8-player (or lower) game from utilizing dedicated servers and local wireless, though; Rocket League's done both on the Switch since 2017.