I know that this has been a long-standing practice, but that doesn't mean it is a good one.
The (savage) raid tiers last about 8 months, starting in an even patch, with the half-way point being an odd patch. Why are we still waiting till the 6th or 7th month to unlock a tier?!
Especially, now we have Ultimates it seems to make less and less sense. Do they not consider that we may want to gear alt jobs? Or maybe we want to engage with the most current raid content (new Ultimate)? Or maybe we want to change jobs/roles for said Ultimate? Or, for those of us with tight schedules, maybe want to engage/invest in other content?
Just doing the math it takes 8 weeks (2 months) to fully gear a static once you clear the tier (possibly a little less so for individuals in PF). That means, if you are in a static, you have to clear the tier in 2 months to participate in the next Ultimate on release (X.1 & X.3 patches). Which seems to be pretty unrealistic for most statics. The more likely scenario is you're clearing the tier in 4-6 months and being time-gated from finishing the tier until the literal last month or so (counting re-clears).
Just unlock the tier on the next major patch drop (X.1, X.3, X.5)