why dont we run DC fast charging stations off diesel or NG generators to lower CAPEX cost ?

The grid upgrade can cost millions for a DC fast charging station.

The inverter to make the DC power can cost 100,000.

Why not skip all this and have a diesel or gas engine coupled to a 400V DC generator, thereby skipping the inverter and grid upgrade? A 200kw diesel engine that is found in a truck is often like 20,000 usd. Throw in the 400V DC dynamo another 20,000, that is 40k for a 200kw DCFS station.

I think this would be cheaper, and lower capex and operational costs. Not to mention, most streets have natural gas lines which could power the diesel engines with a cheap and clean burning fuel. Natural Gas is very cheap around 4c/kwh. A 25% efficient generator, would yield 16c/kwh.