I completely agree - though there are places where I trust an implementation of things like a well known algorithm.

However, to add onto this, I'm consistently shocked at how often it is much CHEAPER to "roll your own." We've done some reviews on systems after a few years and the number of bugs and security vulnerabilities we experience with code based around packages is much MUCH higher. Its hard to put a number to it because the time cost of fixing those issues is variable, but its substantial. Its also amazing to me that it can be cheaper to build your own vs using a 3rd party vendor for something that would appear to be highly specialized - of course opportunity cost is a real thing.