I simply like the ability to be able to control what happens, when and to who and how. Being able to control the flow of the content in games is infinitely better than finding a great vid/comic and it doesn't go the way you want to scratch your itch. Sure, most games are limited in what they offer thus your control is also reduced, but getting to focus on that one thing you like is nice. In irl porn/(3d) animations the gig is over in a short time and that's it, but if you find a game that matches your (often niche) fetish and there's plenty of it with different characters, you will have tons more content (also story, since it's much more satisfying to see how things unfold compared to random porn actors who are playing a role). I especially like open world games such, let's say Violated Heroine, since there's tons of content and you can choose whatever happens to her. Not to mention the legal stuff; it's fantasy after all and not harming anyone irl. Oh and obviously, the ability to create a custom character in some games, be it your ideal person or self-insert is the best.
Tldr, being able to control a character to do what you want is much more fun than watching porn.