The same reason not everyone wears a bike helmet.

Because not everyone thinks the cost/reward tradeoff is worth it.

And there is a cost, in time, annoyance, lack of being able to speak clearly, glasses fogging... The cost is small, but not zero. The benefit is not zero, but arguably small. Bigger than the cost? Most people don't think so.

How is this different from buying home insurance?

Most people have a mortgage that requires them to buy home insurance. They don't have the choice.

But even if they don't have a mortgage, it's still a completely different tradeoff. You can't use "people get home insurance" to draw conclusions on "people should mask indoors". Different risks, different costs, different tradeoff.

You buy home insurance by writing a check once a year. No impact on how you live your life every minute of your waking life. And I can choose to self-insure if I don’t have a mortgage…no mandate.

Masking affects every minute of your waking life, and those you physically interact with. That every-second transaction cost is too high for most, unless immunocompromised. Only ill-conceived mandates make it otherwise, and almost everyone hated them.

Using wheelchairs would prevent falls for young, healthy, normally abled people. The nuisance factor, efficiency, etc., though, imposes too high a cost for the marginal gain from reduced fall injuries.