I'm surprised that I'm about to make excuses for Hanauma bay and the government of Hawaii, but either way I'll go for it.
I visit the Hawaiian islands several times a year for the past few years, mostly Oahu of course but with frequent diversions to the Big Island. The Big Island is my second favorite part of the United states (with the first being the Rocky Mountains). Favorite places to snorkel in Hawaii were Honauau - a special place for me in that I first saw the sun set into the ocean there when I was like 10 years old - and Kapoho. Unfortunately, the former has not been doing well of late, and the latter (including its two meter montipora plates) is now covered by several feet of lava.
Oahu is nice, but to me is just another big US city. (though admittedly the Honolulu suburbs like Kaneohe and Hawaii Kai are much awesomer places than most US suburbs).
Many locals consider Hanauma a great place for a nice day on the beach. The swimming in the lagoon area is fairly calm, and few places match it, especially if you don't want to go to Waikiki. This means you'll see a good number of locals on the weekends. It's also the destination for a good number of (generally Asian) package tours. And it's famous for a lot of casual tourists.
Which means that yes, there are lots of people. The fact that it has lifeguards and the calm water are all good for folks who want to picnic, sunbathe, and get a little wet in a very safe environment. (though with the sheer number of people getting wet and the fact that it's not to far from fairly wild ocean, it is a place with frequent drownings). IMO, this is why they charge for entry, so that some quality level can be kept for the facilities and to limit the number of people. (I've read histories of the place, and there were allegedly even more visitors before they instituted the fees IIRC in the 1990s).
If you don't like that, there's Kailua and Lanikai beaches an hour north. If you swim 100 yards or so from shore in the right places, there are a number of cool patch reefs. (parking will be a bigger chore, though)
The hint for Hanauma is to come early in the morning. This is also generally when the waves are weakest, and if you get in right when it opens (6am IIRC) and before the ticket booths open (7am IIRC) they'll waive the fees. This is coincidentally when lots of hard core snorkelers and divers come (including a 70 year old woman I met who comes almost daily to swim to the fore reef and do her volunteer work)
I first snorkeled Hanauma several years ago. It is very true that there are not so many corals in the lagoon areas. However, I think the fish variety is decent in there. (I have even been surprised by seeing multiple morays swimming in the lagoon in broad daylight).
Nevertheless, even in the lagoon area there are "back reef" type areas near the reef crests with good coral growth. One area is the "keyhole lagoon", which is around 8-15 feet deep. A second area is the front of the "backdoor laggon", where you'll see some decent size massive-form Porites lobatas. You will also pass a 6-foot diameter Porites lutea there, probably 500 years old, which King Kamehameha probably saw when he visited the Bay in the 1800s. Even these coral areas are decent.
But once you pass them - though the backdoor channel, or through the cable channel - onto the fore reef it changes completely. I think the coral growth on the upper fore reef are as good as anything you'll find in the lower Hawaiian islands. But, I think maybe 0.5% of the visitors go there on any given day - because this is not casual swimming, and in fact requires confident swimming of at least a moderate ability; because it's not always possible because of wave action; and because even when you get there it's often not so "fun" because you're getting pummeled by the waves. (my WAG is that the flow's generally something like 300X in reef tank terms when I've gotten there. That's what you need apparently for good SPS growth). Depending on the sea conditions, going further out will bring you different corals. These include some areas dominated by heavy surge with dozens of pocillopora (only safe to swim to on a very good day, admittedly).
I recommend this book for the curious. It's only available used, but the others IMO are nowhere near as good.
https://www.amazon.com/Hanauma-Bay-H.../dp/1566475317
I will try to note these areas on a JPG later and attach it to this post.
Anyway, there is awesome coral growth in Hanauma bay and IMO the Oahu government is right to charge a fee, to limit visitors (though admittedly it is a money maker, and they could do better if they limited package tours).