I think nibbling away is more accurate. There are still no privacy-conscious alternatives to the big 3 social networks (Facebook/Twitter/LinkedIn) and none on the horizon. Yes technological alternatives exist, but not practical ones as I'm not likely to run into someone using Diaspora in real life.
This is similar to GNU/Linux vs. Windows on desktop where Linux gained a little bit of market share but was never a real alternative when it mattered. That defeat is all the worse in retrospect as Windows 10 is now a great vector of privacy invasion for Microsoft.
From a social justice POV, "just don't use the service" may be practical for those with a lot of education and opportunities for employment, but is a non-starter for someone who needs LinkedIn to find work or whose landlord expects to snoop through their Facebook account. We need a solution that helps everyone, not just those with the know-how and economic freedom to use niche alternatives.
I'm not a member of LinkedIn so I'm constantly a bit confused by it. Does it offer anything compelling besides a list of the places you've worked and studied? Why couldn't I get the same benefit by putting up a static web page with a content form? Am I missing out on something?
(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.)
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.
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.
Other problems:
* Services you use indirectly.
* Services your employer uses and reires you to use.
* Services a government service requires use of.
As technological tools become part of the social, corporate, governmental, and institutional infrastructure, "opting out" becomes an increasingly less viable, and more punishing, alternative.
Too: you're denying the specific tools which directly address the situation. Legal and technical means to loudly and clearly state "no", or to sue for damages where this isn't possible.
For example, when all your friends now communicate mainly on Facebook (or WhatsApp, etc.), then your choice is to either lose touch with your friends, or use that service. Sure, nobody's technically forcing you to use Facebook, but the social externality means that you become cut off from your friends in a very real way if you don't.
While that can be a big ask for many services, we're also doing a great job of replicating the functionality of many closed services in an open way. As long as the FOSS/hobby tech world still cares, we'll keep biting away at the new markets closed services create.