In way to many companies, engineers (including engineering managers) have to explain to a non-technical C suite that OSS/FOSS IS NOT FREE and NOT GUARANTEED TO BE CHEAPER than going with proprietary or self-written, minimal, tested and concise solutions in any given context. They can be, of course, and with some engineering investment they can be for the longest time in the feature, but every case is different and a "wave" certainly is not what just removes the need to do this kind of evaluation.
this is not a FOSS question. (i would not touch a closed source library as s potential dependency with a 10 foot pole. it's either FOSS or i write it from scratch)
this is a question of the ability or willingness to adopt and maintain 3rd party dependencies.
fear of FOSS could be added as another reason, but that reason is even worse than mere unwillingness to work with other peoples code.
in order to use a 3rd party application or library as a dependency you must be able or willing to maintain it yourself, in case you run into an issue with its support. (that's one of the big points of FOSS, btw)
you are right about unnecessary features being a risk, but again, that has nothing to do with FOSS as a choice.
There's more OSS than ever but there is a huge lack of stability in most of it.