So, I've been watching YouTube videos about diving in quarries, and I don't get it. A few of them have some fish, and some algal mats, but certainly not to the extent that I have seen in, say, Fishing With Luiza's snorkel trip in a river. Mostly, what I see is abandoned cars and other land-based junk, like visiting an underwater junkyard. If everything I can see in a quarry dive is something I can also see in a junkyard on land, why would I go to the trouble of diving there? What have I missed in these videos?
What you've missed in the videos is the experience, the practice, the learning, the extending of a person's diving repertoire/abilities.
I get it though, I really do. Until last year I had no desire to dive "cold" or "low vis" or "no fish/coral" dives. Last year I decided to "deal with it" at the local quarry because I wanted to take some classes and didn't want to take a vacation for that purpose, so I ended up at the local quarry. It was late fall, so water temps were up in the 70's at the surface, but in the 40's once you got deep, so I surely wasn't looking forward to that, having only dived tropical waters or Florida springs (a minimum 5 hour drive away) type diving previously. What I found diving there for the classes and for fun was that I became a better diver.
Obviously the classes gave me skills and experiences to make me a better diver, but that's not the end of it. I'd never experiences visibility so low before (15 ft not uncommon in the quarry, compared to the 100+ ft vis I routinely encounter in the caribbean/bahamas. That was new, and I didn't know it would impact me in any way other than disappointment. The first time I found myself in the water with no visual reference, thanks to being far enough away from anything that the low-vis resulted in me seeing nothing but water, was very disconcerting. I literally found myself close to panic, but found a way to calm myself, accept the situation, and decide on a rational path forward from the unexpected conditions I found myself in. Now I'm a lot more comfortable in low/no vis environments, and I'm comfortable doing free ascents/descents without a visual reference because I can actually practice those things in that environment, where I would never have had such an experience in the Exumas or Cozumel etc on my vacation dives. So I became a better diver with new abilities/skills and a more well-rounded repertoire of diving experience.
I learned new skills because I can take the time to do a class on the weekend, instead of only doing them when I'm on vacation far away. I've learned to dive deep, and learned to dive in a dry suit, and learned new skills becoming a rescue diver, etc, because I can dive in that quarry. The odds I would have taken those classes on vacation isn't very good because I just want to enjoy my vacation, I don't want it to be "working on classroom parts of courses" or "focusing on skills instead of enjoying the dive".
When not taking classes, I can go with my buddy and enjoy the dive, but more importantly, practice skills. I'm not setting up a camera to evaluate my finning techniques while I'm on a liveaboard dive trip, but I'll do it in the quarry at home. I'm not thinking about practicing a CESA on vacation, but I'll do it when I go to the quarry for the purpose of practicing skills. That $100 2-tank dive isn't where I want to spend time practicing skills - that's where I want to enjoy what the dive has to offer that I can't get in the quarry back home, the $10 dive in the local quarry is a great place to take off and put back on equipment etc just to keep those skills fresh.
Most importantly, though, is I get to experience a dive. I can put on my gear, get in the water, and almost effortlessly glide through water. I can look up and know there's a huge open space full of air up there and I'm breathing down here, surrounded by water. I can pause and enjoy the serenity of the bubbles being the only noise disturbing my thoughts and relaxation. Sure, I can go swim through the hoops, or check out the old excavator at the bottom of the quarry, or the number of other man-made objects there are there for me to see, or the few fish around (and some fresh-water jellyfish when lucky enough to find them around). The best part about diving in the quarry is just that I get to be diving though. I get to enjoy that underwater world that man wasn't designed to be in, and I get to have that experience just a quick drive from home.
Oh, and it costs me $350 for a year's worth of 2-tank diving days... which is a heck of a lot cheaper than any of my vacation diving.