unfortunately i think the issue is more complicated and tied to so many things, but ultimately the idea and image of masculinity, toxic masculinity and homophobia.
too many straight men thing anything not a boxer is 'panties', and straight male dominated cultures [which is most if not all] tend to think of anything else as "less".
We and culture has to actively work on breaking down those barriers, like intimacy with friends [even I dont hug friends, thats something I have to work through], accepting bodies and nudity as normal and not shameful or sexy, and not judging others. We can do only so much with visibility and our own 'activisim' but it's going to take a culture shift, which is slow. and unfortunately, being more accepting of other people's underwear choices and expanding one's own is super low priority, in the state of the world right now
one thing might be to actively ask retailers corporate offices to offer more variety in their stores, offer accessible brands with large ranges maybe, to encourage them to give folks better access and instant gratification compared to online shopping. I know many retailers are losing the battle to Amazon and online shopping, and may be open to suggestions?