Hasn't the establishment been non-conservatuve at least half of the time for the past 20 years?

I've occasionally seen right-libertarian ones (I think historically this has been the most common form of right-wing-ism in hacker-y spaces).

In general I agree, left-leaning ones are way more common. Maybe you are correct regarding the reasons. But I've definitely seen conservative ones too, with libertarian ones being more common among those (e.g., saw a number of "Who is John Galt?" stickers some years ago).

As they mentioned, though, right-wing bumper stickers absolutely are a thing in some places.

Wasn't long ago that opposition to fascism was the conservative position. Why is a sticker expressing the same considered "progressive"?