A lot in porn (maybe all of it) is fantasy, and one of the fantasies that apparently work out is the getting ambushed by some guy(s) and getting fucked.
It works in porn in may instances, especially because the guys doing the jumping are obviously hot. Oh, porn. Creating expectations that seldom come true.
And of course you can find it in mainstream movies too, where it's used in a very different way.
There's something strangely forbidden about these videos. In the #metoo era, they feel transgressive and very of the day.