There are only a few reasons why they would be sticking, rubbing, or mis-aligned; it’s always a sign or one thing or another, big or small, needing a bit of improvement. Sticking doors are often a result of the foundation below shifting.
Your door is typically attached to the door hinges that are screwed to the door frame, which is fastened to the wood framing of the structure itself. When that structure shifts, the door has no choice but to follow.
In the cases of shifting framing, we use the operation of the door itself as a gauge to show us what part of the structure of the building needs attention, and how much; if the hinge side of the door has dropped, then the knob side will tend to rub on the floor; if the latching side of the door (the doorknob side) has dropped, the door will bind at the upper corner on the knob side of the door. Sometimes multiple doors in a section of a house are off and when that is the case, usually some floor lifting as leveling solves the doors at the same time!