Arma is a video game with video game logic optimized by programmers who deal in software.
When there have been attempts at what you are saying they usually fail or are short lived until a better optimized DMR comes along The L86A2 for example, though it lasted a while as fighting dragged out the British moved to the L129A1 and with the latest SA80A3 work have decided not to continue the L86.
The M38 by the USMC followed that logic today but I suspect the Marines will be picking up US Army M110A1 rifles in the not to distant future.
The issue is that the needs of a LMG and a DMR conflict leaving the weapon lacking in one area of the other.
QBB99 was optimized for use as a IAR the high placement of the optic and barrel mounting of the bipod would detract from it's ability as a DMR.
For a DMR you want to have the barrel and Optic with as close a bore sight as possible where in a IAR area effect is okay. In a DMR you want to free float the barrel for harmonics the bipod on the QBB would mess with that. The L86 Which did do something like what you are talking about had to reinforce the barrel with a strut that ran along the under side of the barrel to the receiver to take the weight of the bipod and alleviate barrel flex.
Farther more one of the changes made for some DMRs is removal of the burst or auto sear from the trigger group this is done to improve trigger pull but at the cost of automatic fire.
The PLA designed and built the QBU88 to optimize it as a DMR for there squads. Now yes it's not perfect but it offers more to accuracy then the QBB95. Now yes it might be nice to use the same magazine as the rest of the squad, but it comes in that at the cost of sitting the rifle very high in the prone with a already very high sight line.