Adoption.

Not that many people care/are aware about the privacy/security issues at stake.

It was too much of a niche thing (i.e. not for iphone's "average" users) and from a big enough player that Apple wouldn't protest.

But it was a complicated and long process to install/configure it. I doubt many non-geeks bothered. So it probably never got any traction beyond a few thousand users. Not worth keeping around at Linkedin's scale.