It'll help if we look at the reasons why each are locked up.

Aether is the "raiding" data center. Raiding is a massively popular part of the game, with over 30% of max level players clearing them alone, and that doesn't even account for those who don't clear the tier but still prog.

Crystal is the "RP" data center. RP is a massively popular part of the game, with venues listed on every data center, RP being a popular thing in MMORPGs generally, all to the point of the developers acknowledging it is a massive part of the game and regularly releasing new furniture, emotes, deliberately targeted glams, gpose updates and other misc features like when they added bard music.

Primal is supposedly the "PvP" data center. But I... suspect PvP is not a massively popular part of the game. So that's pretty much why it's not enough to make Primal as locked down as the others. If anything I'd see Primal as a mixture of raiding and RP, and something of an overflow from the others.