When it comes to my personal laptop, I also, typically, blindly trust the keys coming from developers because I don't have time for that. Not so much if I have to deploy a system into environment that several orders of magnitude more expensive than my laptop...
With systems like Python, I'd imagine that a solution to web of trust would be that some group of developers would organize a curated set of packages. So, for the cases where you need better security assurances, you'd use that. I mean, of course there's no guaranteed solution for the web of trust, but, in practical terms, something like that would be good enough for regulators.
There's already stuff like NumFOCUS. They don't particularly focus on the technical side of things, or endorsing more secure practices, but, in principle, they could. Maybe there will also be others once we have been bitten more times by some security breaches.
