Hello,
It's a long story !
But to make it short, having the same feature than HikaShop backend is complicated since a vendor might not be able to see all the products so, in some cases it could work fine but in another, it could be a nightmare (and handling both is confusing).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.