Hunts are meant to be open world content accessible to anyone that is able to find and engage them. To get into Diadem in the first place you need to first buy a resource (a cheap one but it's still an entry fee) and then sit in a Duty Finder queue, which would be terrible for DPS players, or use an FC ship which also means you're not sending it out on exploratory missions and missing out on materials from that. Hunts, as flawed as they are now, are much better than they would be in Diadem and people would riot if you put them in gated content. Would it make Diadem more utilized? Yes... Would it make Diadem more popular? ............ Nothing will really ever make it popular and when the rewards dry up it will die just the same.