Ostia was, as I recall, a major port for the Roman navy. As such it was likely populated by a lot of sailors and their families, as well as support people and merchants you'd find in any port. I wonder if the sailors might influence this finding of unusually high cases of rickets for a so-called small town rather than a city (though as I said, it isn't described as a town).
Investment in the high rises, which had a reputation more like the former Cabrini Green in Chicago, as opposed to Bob Newhart's high-rise in The Bob Newhart Show, were popular among the up-and-comings, like the lawyer Cicero (low birth). There were quite a lot of street level take-away restaurants, because most lower class Romans, while they lived in pretty nice conditions (compared with wattle-and-daub with thatched roofs common in other parts of the Empire), did not have kitchens. High status homes, like the jumbo mansions that survive in Pompeii, had both kitchens and kitchen staffs (99% of them slaves), and a huge variety of food from all over the known world.