Originally Posted by
Boazslom
Thanks I’d just thought when you buy one with United unless you are purchasing basic economy it would auto assign you a seat on purchase and then you could move later. Is this not the case?
You don't buy a specific seat - you buy transportation in a particular cabin. You indicate a preference of seat in that cabin when you select one, but you're not "buying the seat". UA reserves right to move someone after a seat has been selected, although it is rare outside of an aircraft change.
In addition to above reasons suggested in previous posts, seats may not show up front if the flight is overbooked in back.