Mostly because Jensen Huang was willing to pay a nice premium over what the market would otherwise offer. There are some cough synergies cough that Nvidia could

Mostly because Jensen Huang was willing to pay a nice premium over what the market would otherwise offer. There are some cough synergies cough that Nvidia could have instrumented for higher profits, Jensen had a clear and enthusiastic vision about how to get there. Softbank can still sell ARM to anyone including the public market, they just won't get as much money for them that way. Presumably.