If your online game is built around massive 50 to 100gb updates, you need a system that has a guaranteed large internal memory that requires very little optimisation because your game is nowhere near completion when it launches. Cloud gaming will help remove this hurdle.
You have a few other factors such as a studio being pushed to get a new game out rather than giving them time to learn a new platform because you need a new game out every year, so you end up outsourcing it at a higher cost and the outsourced product is lower quality due the Switch not being treated as the lead platform from the start.
But more than anything, it is the file sizes.
If the Switch had larger storage to start with and cheaper cart sizes then it would be a different situation but that didn't happen. So going forward it will only get Destiny 2, GTA Online, WOW, COD, Sims 4, Battlefield or Tom Clancy stuff by having a new system with absurdly large storage or for Nintendo to pay for it or the Switch sales grow year on year for a further 2 years.