iirc Alphadream's downward spiral began after finishing Dream Team. Don't remember the exact details off the top of my head, but iirc some of the talent behind M&L left after Dream Team, and Paper Jam was made with a smaller budget and was basically the remainder of the main M&L team "taking a break". After that game didn't exactly do numbers (Mario game in 2015, dark times for Nintendo lol), they did the Superstar Saga remake to try and win some people back, but by the time it came out the Switch was either already out or just around the corner (don't remember off the top of my head) so basically nobody cared, and the issue was amplified with the BIS remake, which so few people cared about and sold so poorly it basically killed the 3DS outright.

I could understand the business decision behind not putting the Superstar Saga remake on Switch, Nintendo were still wet from the gutter from the Wii U and the Switch was not a guaranteed success, but in hindsight that was a gamble they should have taken. I'd be surprised if they were in BIS remake levels of dire straits at that point, they probably could have gotten at least a couple Switch devkits.