I don't get what the fuss is about being asked to reserve a seat on the shuttle. I personally like the peace of mind of knowing that I have a seat at a particular time. And if I haven't yet reserved when asked, the hotel associate would immediately check and can reserve / confirm one immediately if seats are still available.

And yes, there were times where I've taken the shuttle and it was full so people simply waiting to climb aboard without reservations were turned away.