Simply put, the way the marketplace was integrated on the bedrock edition is completely horrible. There's no reason to buy the vast majority of the content because you have to start a new world with the one bundled with the pack if you want to actually add anything to the game. I (and I'm sure almost everyone else) would be much more inclined to spend a lot more money in the marketplace if we could simply grow our catalog of stuff to add to the game all at once instead of being forced to choose one at most. If I wanted to add both the jungle animals and arctic animals pack at the same time on any world, I should be allowed to, not forced to pick one or the other and only able to do it on the world they come bundled with. It's idiotic design and it needs fixing ASAP, espeically once Hytale comes out and completely styles on Minecraft's modding capability.