Personally I think it is just the timing of the sport. Pride FC had amazing talent that was equal too (or to some fans even better than) what the UFC had when they both existed together. Then the UFC took most of their best fighters when Pride folded, but there was still a large group of fighters that were overlooked or unknown who ended up in promotions outside of the UFC. Also, the UFC wasn't running an event every weekend at this point so they didn't need as many fighters.
Point being, when Strikeforce came around there were still a lot of really good, entertaining, high level fighters that Coker could bring in. Fast forward to today and most of them are in the UFC or one of the smaller UFC feeder promotions like LFA, Invicta, Contender Series etc. Coker and Bellator are basically left fighting with China, Japan, & PFL over young up and comers or old veterans no longer employed by the UFC. To find a young star in their prime is nearly impossible, to keep them even harder. Because of this they are left to do the best they can with what they have, and unfortunately their isn't much available, basically a handful of guys maybe a dozen if we're being generous who could compete at the highest of levels in the UFC.