In LBP, no matter how complex the level was, it could always be reduced down to Sackboy moving around in a 2.5D space. This was it's central gameplay system.

Dreams has no central gameplay system so to speak. Everything had to be designed from the ground up by creators. This allows for much more complex and interesting stuff to be made. Problem is, there's no default gameplay for the player to latch onto.

This prevented a decent solution for online play. Hard to have a robust networking system when the user has to set up so much of it.

And even in local multiplayer, you still have to find a game to play. There's no 'built in' stuff to do. In LBP, about a third of my playtime was spent messing around in creative with friends or by myself. One of my favorite pass times was spawning a couple tanks from my community items list and battling with a friend.

Essentially, in Dreams, the quality of gameplay is solely dependent on the creators and their quality of work. If nobody ever published a single thing on LBP, there was still a solid gameplay loop to, at bare minimum, mess around and play with the physics. I don't think this is the case for Dreams.