What are we "putting up with" and what problem are you trying to solve? LinkedIn works because it provides value. Competition doesn't just appear for fun; it appears because there is differentiated value to be captured.

So once LinkedIn stops providing the value that gives it its dominance, and/or someone finds a way to deliver more value, you'll see your competition. That's your answer. Seemingly nobody has found a good enough angle or opportunity,

And FWIW, sure the network effect is hard to replace, but not even close to impossible. Just ask the dozens of other social networks that have fallen from greatness. It just means a competitor has to deliver outsize value to overcome the inherent network effect that they're competing with.