That's assuming the numbers shown fully take into account all the tangential cost related to the transition, and not just "cost before vs cost after". If you spent 500M in developer hours doing the migration, that just wiped like 10 years worth of savings. Also it's not clear if in 2 years you really get to see the cost of maintenance and breakages. One big breakage could wipe off that 75M very quickly. Of course Cloud also has its fair share of down time, so you'd have to compare longer term to get a better sense.