Still, what do you expect the developers to do? add a handgun version, which is identical to the smg version, but without the burst mode? That’d be useless, nobody would even consider using this gun because it’s just a bad copy of the smg version. A handgun version which can be converted into a burst-mode version? That would either mean that they can spawn with an integrated upgrade, or you’d need, again, 2 different guns which you can change via recipe. All of that is a whole lot of work for little to no gain, if you ask me, so it probably won’t happen, unless you can give a good reason why they should change it.
If it really annoys you, look into the jsons of the game, you could mod the Tec-9, delete the burst-mode flag and change it to a handgun, it would then accept a burst-trigger modification which would add the burst-mode again.
Another possibility would also be to ROlEPLAY it. Just decide if the tec-9 you found is smg-mode or handgun mode and stick with it.
edit: also, speaking from experience: You have a higher chance of hte issue getting fixed if yuo actually mod it yourself - the developers would then just need to merge it with the main game jsons, that would give them less work and you would have your ‘better’ tec-9