Aren't software engineers discouraged from "reinventing the wheel"? Even if they manage to rediscover an algorithm by themselves, their own implementations would likely be bug-ridden and inefficient compared to what would be available in libraries. The whole purpose of libraries is to reduce the amount of code programmers have to write by providing pre-fabricated solutions to various programming problems. If you hired a programmer to build some custom software for your business, would you be happy if he spent his time rolling his own quicksort routine instead of just using, say, the STL sorting routines? Would you give him a raise for hacking his own buggy implementation of arbitrary-precision arithmetic (and make no mistake, it will be buggy) instead of using off-the-shelf and highly tuned implementations like the Gnu Multiprecision Library?
Software is rather like mathematics in the sense that you don't get points for solving previously solved problems. You won't impress anyone if you reinvent how to compute the area under a curve, as some biologist once did (http://academia.stackexchange.com/questions/9602/rediscovery-of-calculus-in-1994-what-should-have-happened-to-that-paper). Results exist to be used by others; otherwise no one would care about them. All those algorithms and data structures in CLRS or any other algorithms book are there so that programmers don't have to rediscover the solutions to various problems.
No you do not use software libraries you bring with you from a university or another company you worked for or found on the internet. You use the libraries which the company you work for owns. In today market you definitely do not use open source libraries since you do not know what restrictions exist on those library for the free use of them. Today they are libraries which required you to freely license back any changes or improvement you make to the code you got from open source. If the code a developer used in a company product has one of these stipulation than the companies entire product can be required as part of the open source from the period forward and it may bare the company from patenting their product or even making money of that product.
This all comes down to IP ownership and control, imaging if Apple engineer use opensource libraries which had requirements to freely license back any improvement Apple made, Apple whole products could be free to use by Google. Yes I know Apple uses Opensource code, but they have people who know the who IP ownership issue watch over what is use. Also Apple was criticized for taking form the opensource communities and not giving back the improvements which they were not required to. Apple only gave back things which would help them move their solution forward, but did not give back what made their products unique.
This is not about reinventing the wheel, it is about not using someone else's wheel which could cause you IP issue down the road.