First of all it would take too much time to find out all the authors of all the software that I routinely use, and then keep up with what their current views are on various topics.
But I think the main reason is that most software has more than one author, and it would be unfair to judge the usefulness of that software based on the (non-technical) views of just one of its authors.
Your reasoning would apply only for single-author software, and TBH I would consider those pet-projects anyway, and I don't think the original author would care much whether you use it or not.
Edit: about gained knowledge:
I think you could apply this if you compare multiple competing solutions, one deciding factor could be the author's thoughts on various topics.
Just like how a company's attitude towards various topics might be influencing your purchasing decision: for example
Nvidia doesn't support open-source drivers, hence I don't buy Nvidia when choosing a graphics card.
But again for me those are all technical reasons, I wouldn't factor an author's/company's political views into that decision, unless it was something really horrible.