Why doesn't Kymco do this

Take the engine from the Venox (but lock the Venox designer up where he can’t inflict anymore damage). Weld up a simple bird-cage frame. Throw on somewhat functional suspension bits and brakes. Bang it out the door for a reasonable price, say somewhere just below the price of a used, legal Hornet 250. Sell 'em to non-wealthy, non-poor schmucks like me who want something a little bigger but gag on the ridiculous prices of imported bikes here. Sounds reasonable to me. Or maybe I’ve just been hitting the crack pipe too often lately…

In Thailand I saw a (single cylinder) 250 engine shoehorned into one of those little step-through scooters they have there. Looked like fun.

I guess the simple answer to your question is marketing. They wouldn’t want to devalue that exotic “big bike”, the Venox!

For a cheap 250 v-twin either Kymco or SYM could simply bolt two existing 125cc OHC single top ends to a new crankcase. With a single carb that would be a cheap and simple engine with a huge supply of parts available that just about every mechanic in the country would be able to work on it without any more training or special tools than he already has.
Why aren’t they going to do that? Because retail prices are supposed to go up, not down.