Not long ago, Bethesda held a panel at PAX Australia 2018 discussing its games and even speaking about relations with certain other companies. At the time, Bethesda's Marketing Executive Pete Hines said Fallout 76 wouldn't be coming to the Switch and it was also briefly mentioned how the MMO Elder Scrolls Online could not fit on the system.
During the same panel, Hines explained Bethesda always liked Nintendo - including its systems like the Wii - but the main barrier was the hardware specs. Fortunately, when the Switch was released Bethesda found a great partner in Panic Button:
So the idea of being able to take something like what we did, looking at the tech specs, and going, ‘That’s actually really close to like what we kind of do now.’ That was always the big barrier for us with Nintendo stuff. It wasn’t that we didn’t like the Wii or we don’t like this, it was just this is the stuff that we make, and as many things as will run that, we’ll do it. So as we looked at the specs, we started looking at games like Skyrim and Doom and Wolfenstein, and we were fortunate enough to either have really talented devs who were also very keen on making it which I think is important or finding a great partner in Panic Button who had the ability to take what we were doing and say, ‘Yeah we can make that happen on a Switch.’
Later in the panel, Hines said during the time the 2016 version of Doom was being developed, the team already knew about the Switch. As a result, they designed the game to be scalable. This paid off in the long-run, with the company able to easily bring Wolfenstein II: The New Colossus across to the hybrid system. He went on to note how the next Wolfenstein would be on Switch and made a nod to Doom Eternal coming to the platform as well:
The benefit for us was that id Tech 6 was really built and we knew about the Switch during the development of Doom 2016, so they were able to make some choices to make sure that it was scalable so that it would sort of not be too far out of line with what the Switch was doing. The benefit there was that it allowed both Doom 2016 to happen on the Switch as well as Wolfenstein: The New Colossus, because that was built off of the tech that ran Doom 2016 so that was sort of a two for one there, and that’s also why the next Wolfenstein is gonna be out on Switch as well and that’s why Doom Eternal was announced. In that case not just as a port, but as something that for the first time we’re building a game from scratch that really has the Switch in mind. That was honestly… that tech allowed us to do a lot of things across two different franchises. I don’t know how the hell they made Skyrim run on the Switch, but they did it. It looks great, it’s fun. I have played more Skyrim than a lot of people, but I still play it on my Switch because it turns out it’s pretty cool to be sitting on a plane and fighting a dragon.
Hines also clarified older games like Fallout 3 are unlikely to be ported across to the Switch because it takes a lot of work to get such titles running on new platforms. As stated above, it's easier to create new games with certain platforms in mind.