For things that the standard library can do, it is usually the best choice. It's code that's already sitting on the user's machine, why use something else?
And also, those are generally relatively straightforward things whose design are hard to get wrong (but there are exception, e.g. Python's urllib). Being a standard library and not a standard framework helps.
For what it's worth, I use Java's standard library whenever possible. It's quite extensive and the fact that the documentation is top-notch makes it a joy to use. That being said, there are still a lot of supplemental things you might want to do, which is what things like Google Guava or Apache Commons are for. But they are to supplement, not replace the standard library.
By the way, some parts of Apache Commons would be a good example of how not to design a standard library, I don't want to piece 10 objects together to do a simple utility function call.
And also, those are generally relatively straightforward things whose design are hard to get wrong (but there are exception, e.g. Python's urllib). Being a standard library and not a standard framework helps.
For what it's worth, I use Java's standard library whenever possible. It's quite extensive and the fact that the documentation is top-notch makes it a joy to use. That being said, there are still a lot of supplemental things you might want to do, which is what things like Google Guava or Apache Commons are for. But they are to supplement, not replace the standard library.
By the way, some parts of Apache Commons would be a good example of how not to design a standard library, I don't want to piece 10 objects together to do a simple utility function call.