This could point at an earlier step in the pipeline - e.g. the recruiters at those companies may have been using LinkedIn as a primary search tool - but that's a signal of its own.
What happens when you have do code features that you won't want to do? No one puts their dogshit, get-it-done-before-the-weekend code on github.
And it's useless for telling me how well you'll do on a team, how you'll interact with other stakeholders, if you're sketchy and will run off with our IP (or just sell creds on the darknet), and if you'll be able to handle high powered office/project politics and their pressures. Linkedin may not be a perfect (or even good) signal for that, but it's a start. Long work histories but no contacts on Linkedin? Okay, not a dealbreaker, but may be worthy of an explanation.