Egos and personal vendettas. Some of these people incorrectly believe because they are a group and part of big organisation, with access to better lawyers, they will win. We know this as "Risky Shift" in our occupations as pilots. When HR departments and managers realise they got it wrong, they just dig themselves a bigger hole for fear of looking like idiots (only to make it worse). I know of 3 recent cases in the last several years where from the word go the employee's case looked way more solid than the company's, but the company pushed it all the way only to get egg on their faces.