It can be both that poster over estimates just how many people have the luxury of choosing who to contract for based on what tools they have to work with.

In fact it seems to me very petty and unprofessional attitude in the first place.

And it would also prevent them from working for any company in a regulated sector or any company that cares about security and information governance not to mention about productivity; I’ve seen plenty of contractors like this being kicked out after the 3 time they missed a meeting because hipstermail or stallmanmail couldn’t parse the WebEx links in the meeting invite, they couldn’t open a Visio diagram or worse we found they were trying to push code into private repos or using some online code beautification services...

Unless you are working on tiny projects as a contractor you are going to be obligated to use what ever tools the client uses, and in fact adherence to the “company spirit” is often more expected from contractors than internal teams that can get some leeway through internal politics.