Gotta strongly disagree that you may as well snorkel if you’re just seeing reefs. It’s a totally different immersive experience while diving. There’s vastly more to see diving than the limited plane you see top-down in very shallow water.
The two sports are quite different -- but the difference in risk profile, costs and equipment required understandably rules out scuba for some.
On non-dive days in the tropics I will typically get up at 6am and start snorkeling right away usually until 9 or 9:30a. My wife says I am first to turn snorkeling into a endurance sport.