Accountability is on the people using a billion third party dependencies, you need to take responsibility for every line of code you use in your project.
If you are really talking about dependencies, I’m not sure you’ve really thought this all the way through. Are you inspecting every line of the Python interpreter and its dependencies before running? Are you reading the compiler that built the Python interpreter?
It's still smart to limit the amount of code (and coders) you have to trust. A large project like Python should be making sure it's dependencies are safe before each release. In our own projects we'd probably be better off taking just the code we need from a library, verifying it (at least to the extent of looking for something as suspect as a random block of base64 encoded data) and copying it into our projects directly rather than adding a ton of external dependencies and every last one of the dependencies they pull in and then just hoping that nobody anywhere in that chain gets compromised.