Discoverability and messaging. If you like hearing from a range of recruiters, putting a keyword-filter-friendly resume on LinkedIn is a good way to make that happen. The quality varies pretty widely, but at least some of them are worth talking to in my experience.

(Stack Overflow Careers is another good spot if you're interested, with in my experience a lower incoming message rate but a somewhat higher average lead quality, and none of the irritation that LinkedIn generally creates in its users.)

> Why couldn't I get the same benefit by putting up a static web page with a content form?

The same question could have been asked of GeoCities and one could give the same answer: most people outside the tech bubble don't know and don't want to know how to put up a website.

Yes, it's "not that hard", but it's also not as easy as filling in a bunch of text fields on LinkedIn - especially when you factor in things like SEO if you have a common name.

Some people find the professional-life-focused networking compelling.

Me, I find it theoretical, due to its profligate handling of email addressbooks and my history helping maintain mailing lists and selling items on Craigslist before they implemented full bidirectional address anonymization. I've had a large number of invitations, likely autosent, to connect from folks I wouldn't recognize if they sat down in front of me.

People confuse marketing with innovation. Ask the creator of sliced "wonder" bread.