Do you have any data to back up this argument? In my experience, energy weapons/explosives/heavy weapons classes are wildly popular in video games. Engineering classes are a very broad space for game design. They don't need to be pet or turret classes or gadgeteers.
Here's a breakdown for WoW's arguably biggest competitor FFXIV as of August 2023:
https://ffxivcensus.com/#class
Machinist is actually more popular than a number of classes.
With all due respect, it sounds as if you don't particularly enjoy engineering/tech class themes (which is fine) and are extrapolating that to mean a majority of other players share similar views. These arguments sound similar to other posters in this thread claiming we can't possibly have an underground or hollow Azeroth expansion because they personally don't like those themes.
I understand not wanting Blizzard to spend resources on something you don't enjoy, but ultimately they will design the game based on whatever features they feel will be most beneficial to player retention and attracting new players. Whether that is adding a bard or engineering class I can't say.