"Switch can't handle those games, and they're not worth the investment to port"
I think a lot of people over simplify this reality. Witcher 3 had a team porting it for a year. It's not to say that it's not worth the investment but if we were to take GTA for example, a huge game. Porting that over, even if just the 360 version would take notable time. Rockstar could instead invest that in new GTA online content, which immediately serves their audience and has a much quicker return on investment. Developers are always working on new things including prototyping their next big thing (many times over), ports are kind of at the back of their mind once they've hit their target platforms.
Games like Call of Duty are pumped out like machines. It completely understandable how they may be apprehensive about convoluting the dev cycle with a Switch inclusion. All that effort for 1m sales when they could make that same money back in DLC for main platforms or if the developer is serious about the experience on their game, they could use that time to ensure the quality of the main versions and avoid delays. For things like Call of Duty mobile, these are decade long investments which make for very underwhelming console experiences. I would understand if they were porting the yearly COD to mobile, but mobile has its own platform specific game that will keep them going for a while.
And then there are developers who simply do not want to compromise their experience. Porting games to significantly weaker platforms is not fun.