I agree with you in principle and in the past only accepted connection requests from people I know as well. However, I think LinkedIn's promise as professional social network has really diminished over the years and mostly functions as nothing more than a job board at this point. I probably have about 100 recruiters I have never met in person in my network. As a contract dev updating my profile serves as a way to push notify these people that I'm in the market. It's really the only value I see left in the platform.