Huh?
Pfizer is the one who submits for approval, not the "FDA"
The rules that have been in place for decades require a specific followup timeline before you can submit. This is precisely WHY the EUA laws exist, so that something can be approved provisionally in lieu of this timeline.
Pfizer just submitted for this about a month ago, IIRC. It's not a "rubber stamp" here, they need to follow the existing rules, laws and practices in place. Priority has been on getting EUAs for younger age groups approved, so that the vaccines are available to them sooner.