I have to call this out as a bit of a hyperbole.
They already participate, quite openly, in security audits[0], and while yes, I'd love it if it was OSS too, but the reality of making money on these services is that (especially I believe at the time 1Password was founded), is it wouldn't have likely done them any good, really. In fact it could hurt their business. I believe 1Password was one of (but not the only!) pioneers of this being a successful consumer business.
Notably, I don't think its worth detracting from a fantastic product based solely on the license of its underlying software. I'm also not aware of any 1Password data breaches.
As far as exporting goes, you can simply generate a CSV file (or plain txt)[1] as well. Not sure what the issue there was, I'd be curious to know.
While I like OSS too, and prefer it when able, I think its a stretch to say they're holding their users hostage if they want to migrate away, not to mention being OSS isn't really a predicate as to whether the software & user experience is actually any good.
disclaimer: I don't work for 1Password, but I've used it for over a decade.
[0]https://support.1password.com/security-assessments/
[1]https://support.1password.com/export/