I’ve genuinely never had a problem with it. If something is wrong, it was always going to be wrong.

Have you worked on a production code base with more than a few thousands of lines of code? A bug is always going to be a bug, but 99% of the time it's far harder to answer "how is this bug triggered" than it is to actually fix the bug. How the bug is triggered is extremely important.

Why is it preferable to have to write a bunch of bolierplate than just deal with the stacktrace when you do encounter a type error?

If you don't validate types you can easily run into a situation where you write a value to a variable with the wrong type, and then some later event retrieves that value and tries to act on it and throws an exception. Now you have a stack trace for the event handler, but the actual bug is in the code that set the variable and thus is not in your stack trace. Maybe the stack trace is enough that you can figure out which variable caused the problem, and maybe it's obvious where that variable was set, but that can become very difficult very fast in a moderately complex application. Obviously you should write tests, but tests will never catch every weird thing a program might do especially when a human is involved. When you're working on a moderately large and complex project that needs to have any degree of reliability, catching errors as early as possible is always better.