I'm not in a senior role. I do enjoy my job but I'm basically a sole Rails dev - I develop an app that the company offers to clients, which I suspect plays into the long notice period - I suspect they'd have a fair amount of difficulty replacing me.

But yes I suspect that's part of why they have such a long notice period - when I've spoken to recruiters / hiring managers elsewhere they're interested right until the point where they discover I have a three month notice period.