This is another form of that popularity defense which I detest.
Lisp being implemented in C has nothing to do with popularity. But it has quite a bit to do with the comparative "open future" of the two languages when one is required, or even simply preferred, to implement the other.
The C standards may not change much, but they're littered with undefined behaviour which still bites programmers today.
Undefined behaviour in C is generally a purposeful decision to not define a particular behaviour in a particular situation, not some lurking secret that bites programmers. Regardless, Lisp has its own undefined behaviour to contend with so this isn't something unique to non-Lisp languages.