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Medical ethics focus on the benefit to a specific individual - your patient.

This defuses the "Should I kill one to save ten?" moral dilemma - the individual is your patient, even if the other ten are also your patients, you must not harm the one. But for vaccines it also means that the wider societal implications are not ethically relevant

So, medics won't recommend that you give patient A an intervention which is of no benefit to A but is really helpful for everybody else. For example, that you vaccinate teenage boys in the expectation that this way they won't infect teenage girls (with whom statistically many of them will have sex) with an STI that harms those girls.

As a result, the guidance cared about proven benefits to you even though taken neutrally you might have been enthusiastic about a vaccine that might or might not protect you but is definitely a good idea for the wider population. The initial studies understandably focused on the numerically larger problem: If we vaccine young female patients does that prevent relevant HPV infections, and then, as a proxy we might assume they also won't get cancer. Such studies can't tell you whether it prevents men getting cancer because that wasn't measured.

So the recommendation to vaccinate boys was delayed because first somebody has to study what might seem obvious - does the vaccine also prevent HPV related cancers in males? It is, after all, possible that some subtle mechanism means the vaccine isn't effective for this purpose, and it would not be ethical to give schools full of boys a vaccine that they personally do not benefit from having - even if societally maybe that's a good choice.

Beyond the female/ male differential, for adults and older, it's basically a stats game. Most adults have sex. Having sex means you're likely to contract HPV, more sex, more exposure. Is it worth getting vaccinated when there's a 50% chance it's useless? How about 95%? 99.5%? Do you always wait for the crossing lights? Did you ever drink beer or eat bacon ?