Sure, but what does that mean, to the actual end product? Do you have any examples? I’m not a game dev, so to me, I would naively assume that these wouldn’t be limiting, or laughable, as the original comment suggested.
jai's author, Jonathan Blow, always creates a game from scratch. His games: Braid (highest rated XBox Live title when released, "Xbox Live Arcade Game of the Year", https://www.youtube.com/watch?v=YgGeBOC0PX4) and Witness (while not winning significant awards, regularly appears in Best of Decade games lists, https://www.youtube.com/watch?v=URjb3RBIe7c).
Besides that there are multiple games where people use their own engines:
In general, once you know what you're doing it sometimes pays to develop your own engine that is specific to what you're doing. Unity and Unreal are generalist enines that you still to bend to your will to do what you need to do and may have opinionated setups of things that are hard to work around, or maybe are omitted from the engine, or just plain don't allow you to do.
