My situation is probably not applicable as regards to hay. Even though we live in a very metropolitan area of Los Angeles, we live only a few miles from a feed and grain store because of an upscale neighborhood where people have horses. So fresh hay is not a problem.
We feed our house rabbits hay, green leafy vegetables, pellets, and treats. I try to buy pellets without molasses or sugars in them because I don’t want the rabbits to get fat eating pellets. They eat mostly hay and vegetables. The pellets are intended for them only if they get the munchies if they’ve eaten up all the veggies and they’ve tired of the hay. There’s nothing wrong with feeding rabbits sugars in the form of treats but everyone says moderation is the theme. They enjoy sugar and easily metabolize it, but it’s too high in calories for them to eat as anything other than a treat. Our bunnies now enjoy fuji apples from the farmer’s market. They don’t like fuji apples from the grocery store! They get small slices in the morning and evening. They also enjoy a slice of banana. They like their banana with green skins with traces of yellow…they like a tart taste along with the sweet. Their like for sweets is a strong motivator for them to socialize with us. If we sleep in on weekends, both of them will be scratching on the bedroom door at dawn expecting their morning treat!
Interesting to me is that after I’ve seen a rabbit wolf down banana/apple until she was satisfied and then leaving some of the treat behind, the rabbit would immediately start eating green veggies. The sweet treat is metabolized in the stomach between the esophagus and the small intestine, but the sweet treat does not feed the cecum stomach at the juncture of the small intestine and large intestine. This is where their symbiotic bacteria live. It seems bunnies have an instinctive urge to eat to feed their symbiotic bacteria. This bacteria cannot live on sweets, it needs the cellulose in hay and veggies. Rabbits must keep the symbiotic bacteria alive if the rabbit is going to live. Their symbiotic bacteria in the cecum stomach transform cellulose into glucose. The glucose feeds the symbiotic bacteria and the excess glucose they make feeds the bunny.
PS: Can’t claim to be an expert, but this is what I’ve read and certainly observed.