Not sure what licensing has to do with software engineering or system design.

I’m sure there are proprietary systems with fewer memory safety vulnerabilities than Linux (and many others with more).

It's got nothing to do with the licensing, but it used to be 'with enough eyes all bugs are shallow' for code developed in the open.

Now, open code allows anyone with tokens to burn to analyze it for hidden weaknesses. That makes publishing code a risky move unless you've already invested a lot of effort in securing it.