The marketplace was just launched around 1-2 months ago. It’ll take time for it to begin to populate. UE4 just came out earlier year, and (someone correct me if I’m wrong) beta access was only for a couple months earlier and was limited to who could participate. I believe Epic has stated that they’re looking for ways to make the submission process much quicker, somewhere around on the forums. It will no doubt get better as time moves on.