My take on this:
What, if the "negligence" of the Alliance isn't due to FD's "laziness", malice or simply hate towards this faction?
What, if FD has something planned with the Alliance that simply isn't implemented in the game so far?
THARGOIDS, anybody?
We already have many, many ships in the game - and new ships are still on the list and known (Panther Clipper, Beluga Liner), others may be planned.
How many more are reasonable?
What, if ranking in the Alliance wouldn't affect ship accessibility at all, but rank-restricted modules (or weapons) instead?
Remember, the Alliance has a good standing with the Thargoids according to the Elite lore. Is it unthinkable, that - once those aliens are implemented in the game, the Alliance will rise to a never known importance? That it will have access to some exotic (non-human) technology? And granting this technology only to reliable commanders in their military?
TL; DR : new ships are nice and good, but rank-restricted ships are simply "more of the same". Who wants this? Why not introduce rank-restricted modules/weapons instead and enjoy a more varied game experience?