From my understanding by talking to sexual health nurses, doctors, the 45 yo cutoff for Hpv vaccines is down to a few things.
Mainly, as the virus is routinely spread about through sexual activity, most over that age have had several, or many sexual partners, each carrying different strains
Once a strain is inside you the vaccine has no effect on it.
There are in excess of 100 variants.
A few are harmful and can cause problems.
A few will give you less harmful but unpleasant things like warts.
Most are benign and are readily spread about with different partners.
So its effectiveness goes down as your age (and number of partners) goes up is I think the nub of what they were saying, and there is obviously the cost of the vaccine too.
A good friend, 50’s, opted to pay for the vaccine as she’d had abnormal cells detected on a sample. It was iirc around £400 for this, but absolutely understand her thinking in doing this.
Its good to know our kids are now getting routinely vaccinated before they get to the age they’re encountering this virus.