Reserved Seating Frustration

I swear every time i use public transport someone is sitting in my reserved seat. It drives me insane. I book a seat for a reason, because that's where i want to sit!! I almost always point out it is my seat but will begrudgingly sit elsewhere.

My question is why do people think they can just do what suits them and sod everyone else? Don't get me wrong if for example the seats reserved for part of a journey and you need to charge a phone go ahead and charge it but move when you get to the reserved seats destination! Rant over