Hardware limitations I imagine, FF7 Remake is on two blu ray discs which holds way bigger files then any Switch cartage and I suspected they may have tried to port FFXV to Switch considering how many FF games are on the system plus the existence of the Pocket Edition port and porting the game to Stadia for crying out loud, but weren't happy with the results with how it was performing on the hardware. Though I fully expect both FFVii Remake and FFXV to get ports for the Switch's successor, same goes for a lot Capcom's current gen line up mainly the Resident Evil games like 7, the remakes, and maybe 8.
I actually think the cartridge space issue and costs are a much bigger reason than graphical limitations because they don't need the bad press that comes with downloading large chunks of the game and cartridge costs for 64 gigs is too high. For graphical things, they'd figure something out.
Just a guy who doesn't want to be bored. Also