Honestly, considering that both GTA IV and GTA V were available on PS3 and Xbox 360, the Switch could very likely run both games considering the system is more powerful than both of those systems.
The only problem, at least as far as GTA V is concerned, is that most of the money R* makes from the game these days is from GTA Online and the Switch couldn't handle that (like there's a reason why GTA V on PC nowadays is over 100 GB in size, it's cause of all the content updates for the online multiplayer - meanwhile the Switch just has 32 GB internal storage for the OG and Lite and 64 GB for the OLED and while you can buy microSD cards, no one is going to buy a 128 GB microSD just for one game, y'know?).
And sure, there's probably lots of people who'd still buy GTA V on Switch even with just the single-player and no multiplayer at all, but for Rockstar, it probably ain't worth the effort (even with the Switch being the 3rd best selling console of all time) considering they wouldn't be able to squeeze money out of Switch owners with online stuff.