Why ever not? it could be very cheap and use a basic piston/turboprop engine while allowing carrying a proper payload.
Because such a big target would be trivial to shoot down, so why waste any sort of engine and airframe and HE payload on something that is going to get blown up mid air... it would make more sense using actual cheap target drones they use for training AD units fitted with heating elements and corner reflectors to give the impression they are bigger targets than they actually are to attract enemy fire.
When the enemy launches weapons to attack your super cheap drones you can monitor them and their launch locations and either release weapons from much higher up in HALE or MALE drones, or send the coordinates for attacks by standoff weapons as soon as possible.
Why **** around with a piston engine powered heavy aircraft bomb when their Navy like has hundreds if not thousands of old obsolete subsonic and supersonic anti ship missiles with half ton to a ton HE warheads.
After these target drones deplete enemy air defence and standoff attacks deplete them even further then launch Kh-22s and lots of other older missiles no longer used... a simple upgrade with new guidance system was applied to all their anti ship missiles so upgrades for ancient obsolete models should be easy and cheap and compared to a piston powered drone maybe travelling at a few hundred km per hour, some AS-5 or AS-3 or AS-4, or even AS-1 or AS-2 is going to make a good sized crater, and using them up is cost effective and frees up space for newer stuff.
The Soviets were good at that... even ancient AT guided missiles were used to drag out HE lines of charge for clearing minefields... nothing needs to go to waste.
With precusion guided weapons, Orion is already very good. It can take out 4 targets.
From altitude even a rocket pod carrying 16 x 57mm rockets with laser homing heads and perhaps a wing to glide a decent distance could be useful... the new 57mm rockets have much more substantial warheads and from heights a wing could greatly improve their reach, and of course the drone will already be equipped with optics and laser target marking equipment, but hopefully MALES and HALES will operate quietly just looking for targets and passing those on to lower flying drones or shorter ranged suicide drones or nearby friendly air power or artillery... the whole purpose of long endurance (the LE in both designations) is that it can remain on station for a day or more, but with ordinance that loiter time is reduced and the actual weight of what it could carry is not amazing... makes more sense to use it to find targets or the buildings they are operating from.
Note a recent post on drones mentioned that Orc artillery was not immediately attacked when spotted because they wanted to observe them and learn the tactics they use and where they hide and where they rearm and repair so they can destroy those locations too.
Blowing up one M777 gun is nice, but following it to the building where it is repaired and where ammo is stored and other M777s are based and trained crew to operate those gun units are all located so you can take it all out in a much bigger strike is even better... even if bombs and missiles hitting buildings is not as exciting as hitting M777s placed in the field.