Being able to pick what biomes when creating world

I've always wondered why this isn't a thing. When creating a world you can pick from normal biome selection or a single biome. I love the single biome but it has me wondering, why not add a custom biomes option? I would absolutely love that as an option and I looked and people haven't even made mods or datapacks for it. I feel like it would be a great idea for people (like me) that want to play in an all ice and snow world, or all mountains and beaches world etc with full customization. Maybe even make it so you can pick which cave biomes you want to include as well if I only want ice caves in a ice and snow world.