> might be able to do purchasing decisions based on used components, their CVE/etc. history, or sheer amount (in less being generally better, unless there is a reason to suspect the vendor e.g. rolled their own TLS instead of using one of the usual suspects).

Counting CVEs is a poor indicator. It's not a pure function of how many vulnerabilities exist, it's a function of how many exist, are found and reported. Those latter two components have a strongly economic nature. It's cheaper to not search and report than be fastidious.

If anything, more CVE reports from a given company is a positive signal that they give a damn.

(There's also the problem that CVSSv3 is not a very sound measurement of risk. It's sorta-kinda just made up without derivation from a sound theoretical foundation, nor is it based on data about actual impacts. The scores don't move smoothly as a continuous function but jump around a fair amount. It's very easy to swing between widely-separated named categories with a bit of argumentation.)