Ever felt like you are dealing with 3rd party jars and library's more than you have to ? They may make things easy but they come with a lot to know and nasty bugs that you have to track down. I believe making the decision of using a 3rd party jar, or building the solution yourself is not an easy one.
On the one side of the problem is you don't want to reinvent the wheel and use the established solutions. On the other hand those libraries comes with lots of features that you don't really need, they may be well tested but still you will probably run into some hard to tackle problems and bugs, for the last the development team would have to learn to use the library properly.
Adding a new jar to the classpath should be carefully thought based on, how much you already know the library, will it be a overkill to add the library or are you shooting birds with rockets, make sure you are not just using because it’s a popular acronym, and what will it really cost me to develop right to the point solution.
And at least my little hypothesis "while the developer per jars goes to zero the more complex and unmanageable becomes your project".