Many people act as if using Open Source libraries did not have any cost. That's not entirely true.
Your developers still need to spend time on trying understand how the library works and often the documentation is missing lots of things or even incorrect.
They still need to decide which library to use.
There are bugs in the library that they will have to deal with.
Some features you need from the library might be incomplete or missing.
What do you see as the cost of using Open Source 3rd party libraries?