The variety of reasons for which different people dive.
Yes, diving - for some - is very much about what you see underwater. Diving - for some - is also about what you do underwater. Several posters have pointed out that quarries offer good opportunities for training, they provide a chance to dive when an ocean is simply not accessible (distance, time,. costs, conditions). There are other reasons as well.
For me, EVERY dive is a training dive. On every dive, whether I am simply an underwater tourist that day, or I am teaching others, or I have some particular mission to accomplish (equipment recovery, for example), I am training myself, on something. WHERE I do that is not necessarily relevant for the most part. In going underwater, I am probably just as - if not more - interested in the process of diving as I am in what I encounter when I dive - gearing up, swimming, blowing bubbles, maintaining buoyancy, managing trim, etc.
Like you, my early reactions to quarries was not altogether positive. I did my OW dives for certification in the ocean, and loved it. I then dove in a quarry and came away think, 'At least I got wet, and breathed underwater. But, I don't need to go there again.' Yet, I did. And, as the years progressed, I found that the quarry where I had previously complained about visibility, and swore never to visit again, was actually quite a vibrant ecosystem, that rusty metal structures were reassuring navigational landmarks, that fish behavior in a quarry is just as fascinating as fish behavior in the ocean.
