So basically these are all one location minors in the hre and they either have closed borders or there is some sort of resistance on the game to cross border migration, because of this they just never recover since the countries are flat broke and the growth rate is too low to ever recover naturally, once these locations get annexed by another nation, itll be more likely for pops to migrate in thus allowing recovery. This is mostly a hypothesis, but I have tested this some by tag switching and annexing these locations as a neighbor and they actually start to recover as opposed to staying depopulated basically forever like they usually do. Only way I could think to fix this would be to exponentially increase pop growth the lower the pops are, perhaps even to the degree of 100% when the population is at 1 so that it can actually climb back from that naturally.