What about the cost of the power and cooling to run the machine (a lot!), and the staff to keep it running?
A100 TDP is 400W so assuming 4kW for the whole machine, that's a little more than $5k/year at $0.15/kWh. Again, the difference is in the tens of thousands per instance. Even at 50% utilization over three years, if you need more than a dozen machines it's much cheaper to buy them outright, especially on credit.