I don't think that I've ever once played in a campaign that had a clear win condition. Even ones with an obvious main antagonistic force (which was far from all of them) were never obvious in how they would actually be beaten. Most people I've played with aren't intent on winning the campaign so much as they are intent on experiencing the campaign (and by logical extension, survive it). I doubt it's that unusual for players to view a campaign as a story expressed through obstacle courses rather than obstacle courses contextualized with a story.
Now obviously in the shorter term, "survive the campaign" does imply "win the encounters." But playing to not lose is a relevant philosophical distinction from playing to win. The implied onus to excel is significantly more lax, and all that's really needed is to not be actively incompetent (which really should not be that hard).