Maybe you are just getting rolled by your suppliers.
According to the NATO report that appears to be the source for the figures in your graph, the USA spends roughly the same proportion of its defense budget on each major category - personnel, equipment, infrastructure and 'other' as the United Kingdom; and according to table 6 in that report, the US gets 1,440,000 active duty personnel for their money; the Europeans plus Canada get 2,000,000 active duty personnel for their dough - so while the USA may spend 70% of the total cost of NATO, that expenditure only provides 41% of the forces.
To put it another way, to get the same total of 3,440,000 men under arms, at the prices paid by the non-US members of the alliance, would cost only 55% of the current NATO budget.
The US pays more, not because it contributes more troops, but because it pays vastly more money for each troop it contributes than the other members of the alliance. I suspect that the take-home pay for soldiers doesn't vary by anything like enough to make all of the difference; but it wouldn't shock me to discover that corporations who supply the armed forces with everything from vehicles to uniforms, and from weapons to rations, make a shitload more profit per unit sold to the US than they do in sales to other NATO member states.
If the USA took its 72% of the money and went home, the rest of NATO would need to find only twice what they currently spend, in order to keep a similar number of similarly equipped troops ready to fight.