Well Im not expert, But i would assume it comes down to the parts used to make the engine.
The old saying is you get what you pay for. Lets be honest here, 95% of CFMoto buyers base a big portion of their buying decision on Price.
They are cheap. Granted they are no Ebay Special, but still a cheap UTV nevertheless. If you want to spend the money one a Polaris or slimier, you get the HP you are talking about. Im not sure about your county though, but here in Australia, a Polaris is literary more than double the price of a CFMoto.
Higher price is due to higher costs. Further engineering and development. Higher quality parts. It may well be the small things that add up.
A better ECU program, better injectors, higher quality steel capable of taking more heat. The list could go on and on.
But as I said, this is simply an assumption by myself.