I see it like this: yes, it's a poor website which comes down to semi-legitimised spam. However, recruiters already were semi-legitimised spam, and they like L

I see it like this: yes, it's a poor website which comes down to semi-legitimised spam. However, recruiters already were semi-legitimised spam, and they like LinkedIn because it's easier/more signal vs noise for them. Employees like it enough not to quit if there's a potential new job. Signal vs noise is not much different from dealing with job hunting/recruiters outside of LinkedIn. Network effects take care of the rest.