Not necessarily. A frustrated developer posts about it, it catches attention of someone who knows how to use Ghidra et al, and it gets dug out quite fast.

Except, with closed-source software maintained by a for-profit company, suck cockup would mean a huge reputational hit, with billions of dollars of lost market cap. So, there are very high incentives for companies to vet their devs, have proper code reviews, etc.

But with open-source, anyone can be a contributor, everyone is a friend, and nobody is reliably real-world-identifiable. So, carrying out such attacks is easier by orders magnitude.