Spot on! We think a language lacks libraries whenever we look at a language which has not been among the language of choice in our area of interest.
> Re. MSVCpp - Not only I got a free version from university (and another one from another university), there's a starter edition (not sure about the name - express?) which is free.
You surely are a young gun ^_^ MSVC++ has been a successful commercial product for a long time (and still is). I think MS made it free just because it started feeling the heat from GCC and didn't want to lose share. However, we were talking about open-source implementations, not free ones.
> Without context, it's hard to say why are they willing to pay.
If you were to hang on comp.lang.lisp for a while, you'd learn that CL do really prefer CL to any other language because of some features intrinsic to CL itself. Moreover, it looks like when they are freelancers, then they are making a good living, therefore having to shell out some cash for their own convenience; if they are employees, they are experienced enough to make the decision about what their company should buy. Why struggle to install a CL environment? Just shell out €1200 and you're up and running with Lispworks CL (among others).
Re. MSVCpp - Not only I got a free version from university (and another one from another university), there's a starter edition (not sure about the name - express?) which is free.
Without context, it's hard to say why are they willing to pay. Maybe it's because they liked the environment? Maybe it's because their codebase is so big they can't switch anymore? Maybe because free alternatives suck at some level? Maybe the company pays and noone asks why? There are so many potential reasons, we'd need to analyse some stories of why are people doing this.