Corrosion!
The post is chrome plated steel, the floor receiver is either alum or some type of pot metal. They tend to corrode. I would try squirting a little liquid wrench, WD-40 etc. into the top and the bottom and let it sit for a while. Then start banging on the bottom of the table with your hand. It should release on one end or the other.I assume that you are in a salt water environment. We are in fresh water, but we still have this problem. I never drop my table, cause I do not want that many people sleeping on my boat, but it should allow the table to sit between the two seats. The table should have a couple of cleats that hold the table in place and prevent it from sliding fore/aft.