As a Skyrim enjoyer and Fallout enjoyer, there isn't actually a reason to not simply like both and play each depending on what they each offer. This manufactured tribalism always comes off as bored shitposter and not sincere. The average person simply likes both.

Fallout4 does have the advantage of being several years newer however. They got positive feedback from Skyrim about companions, so companions are more fleshed out and have stories and combat tactics and such. They also had the hindsight of what mods are popular, and several of the most popular skyrim mods became base game features in F4.

One thing I enjoy about F4 is that it's a crafting/building game when you want that, and then it's a bethesda style adventure game when you want that. I've spent more time in F4 doing minecraft things than I've spent in minecraft itself. Or I should say Satisfactory instead of Minecraft, but you get the idea.

I think the preference for one over the other is almost always going to come down to preference over setting. It's the classic fantasy vs scifi/guns. Gameplay is pretty similar, exploration, quests, it all has a lot of overlap. It mostly comes down to whether you want a gun in your hands or a bow, or whether you want to fight a guy who shoots lightning because he's a wizard or because he's a radiation monster. But it's all the same under the hood if we're being honest.

Contrary to what is repeated here, there actually are lots of good waifu mods and clothing mods for F4. My F4 install had about 650 mods and I did my due diligence researching what I wanted, and there's not really a meaningful difference in quality or quantity. You can make a cute waifu and dress her up in either game, and you can also make a cool dude and give him armor in either game.

As a fantasy enjoyer, I tend to gravitate slightly more towards Skyrim, but I still have 1900 hours in F4.

Ultimately, F4 doesn't have Serana, so it was over from the start.