The models and animations are definitely appreciated, but it leads to fragmentation on the marketplace - after a certain point, the models and animations become less useful as the marketplace grows. It seems as though one of the key principals of the marketplace is to keep things consolidated to the UE environment, and the Mixamo assets don’t fit all that well currently.
For example - if I bought one of the pending animation movement sets that will be available on the marketplace, and found out they were unusable with one of the Mixamo assets, I’d be pretty upset. It might be slightly different if Mixamo offered more animations for UE, but the end result is still the same, fragmentation and a non-modular assets.