Whatever the threshold is, that number does nothing to ensure that low payroll teams spend more than the bare minimum. The top end cap means more overall spending from the big market teams but means little to the teams that don't spend, and does nothing to make them spend. But some owners both don't want to spend at all and want to keep other teams from spending too. That's my rough understanding. A cap w/o a floor does nothing to balance spending across the league or aid parity.