I always unscrew the valve and then press it to release some air before I attach the pump. Currently one of my tubes accepts air immediately and the other one acts like yours. I just keep pumping until it accepts air or I can't pump anymore. Occasionally it takes a second attempt. I have learned that if it has some pressure in the hose the valve will open up and let air in after a couple of seconds. Rarely do I have to make a second attempt since following this procedure.

If releasing air before you attach the hose does not loosen the valve enough to air up the tube without hassle then the tube needs replacing. As long as you have the chuck attached securely it is not the floor pumps fault. At least that has been my experience.