If you're going to look at engineering as a money making profession, then yes, absolutely, I agree with you. But just like there are more "stats that matter" than pure damage per second, there are other reasons to pursue a profession other than just money. For many classes, but I'm thinking of one in particular, engineering can fill gaps in your class that almost nothing else can fill. Take for example the Paladin class. They have no ranged attack ability, but with a little time spent in engineering they can make throwable explosives. Yes, the cooldown is evil, but... if you're soloing with a paladin, you don't have the boomerang, and you need to pull... don't you think you'd find that handy?
Furthermore let's remember that engineering is the profession of choice for PvP twinks! If you haven't made a twink for Warsong Gulch in the Level 19 bracket, let me remind you that there aren't a lot of head pieces in that level! The Green Tinted Goggles from engineering are widely regarded as the second best level 19 twink piece next to the Lucky Fishing Hat which requires a lot of fishing and a lot of luck in a level 30+ zone.
At later levels, the Field Repair Bots are very popular as well, even though they are somewhat expensive to make. Any engineer who can throw one down in an instance will surely make friends of the people who didn't want to hearth home, repair, and come back.
Engineering is not for everyone, but it sure is for anyone who wants to have fun and laugh a little. And while you won't be joining Azeroth's Fortune 500 anytime soon as an engineer, you will get lots of unique stuff over the course of your engineering journey that will help you in the game or - at the very least - give you a good laugh.