1. If there is someone that LinkedIn doesn't seem fit, there are three clicks necessary to make this person fit compared to one click for accepting the rejection. And it is visually made very clear that this person is not fit.
2. The fitness as calculated by LinkedIn it not working correctly by flagging too many people as being unfit.
As a result, inexperienced recruiters or HR staff would blanket disregard these applicants even though a lot of them are much more qualified than non-flagged applicants.
[edit] Here is the overview I created at the time. One might argue that the sample is small. But I think it should be possible to speak to applicants in this case. https://i.imgur.com/n7i5VtP.jpg