The worst part is that WinRAR does not have autoupdate built-in, so millions of people will remain vulnerable for years.
You can argue for your political beliefs, sure, but let's be honest and not claim that there are any security benefits.
What's more, doing security review is very hard. You can't just casually read a bit of code. You need to deeply understand the surrounding context. People who have the capability to do that aren't going around providing that service for free.
-- More reading for the curious: https://www.explainxkcd.com/wiki/index.php/2347:_Dependency