[rixed]

Rephrasing to make my point clearer: you open a performance bug against, say, a C program more often than against, say, a python program, because performance is more likely to be a requirement of a C program than of a python program.

Similarly, again for performance reason, your average C program will have more concurrency than your average python program, therefore also more bugs.

Another way to put it: you use C when you have a complex problem to solve and python when you have a simple problem to solve (unless you are a masochist or a purist I suppose). So, one reason those languages have more bugs may just be that the programs themselves are more prone to errors (which might only be slightly related to size, if at all)