If you’re not sexually active, is it still worth doing?

Yes.

“The route of HPV transmission is primarily through skin-to-skin or skin-to-mucosa contact. Sexual transmission is the most documented, but there have been studies suggesting non-sexual courses.

The horizontal transfer of HPV includes fomites, fingers, and mouth, skin contact (other than sexual). Self-inoculation is described in studies as a potential HPV transmission route, as it was certified in female virgins, and in children with genital warts (low-risk HPV) without a personal history of sexual abuse. Vertical transmission from mother to child is another HPV transfer course” [1].

[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC7579832/

Yes. While direct genital contact is the highest probability way to spread it, any skin-skin, skin-mucosa, skin-object-skin contact can potentially spread it. Consider how much you trust others to wash their hands after using the restroom. Low probability, but possible.

You’ve got a low probability of getting polio, but there’s no reason not to be vaccinated if you can.

Even if you already have a strain, there are multiple types. In fact, people who got a vaccine early on, should consider an updated shot for more complete protection.

The protection from the vaccines lasts (probably) a lifetime, and HPV is quite widespread because it is: very easily communicable, and infections linger for potentially long periods of time without any obvious symptoms

Something like 80% of people are sexually active at all will be infected with HPV at some point. You may not have been sexually active, but your future partners may have been. I personally have a friend who went through stage 4 cancer contracted from her (now ex) husband.

So, of course not literally everyone needs to take it, assess your own risks, but it's quite an easy, highly effective vaccine: don't overthink it.

Life is long and unpredictable, while the cost is very low.

If you ever intend to be, yes.

Yes.