Perhaps the amount of foodstuffs and water needed to sustain a large number of people shrunk as far as storage space was concerned?
With the advent of food synthesizers and then food replicators in the 24th century, the amount of space for other things apparently grew as did the number of folks that could be kept alive for longer periods of time.
(thus the 5 year missions?)
Yeah, there seemed to be a significant amount of cargo storage aboard the NX-01 and crew quarters were very small, even Archer's. It appears a huge chunk of the primary hull was devoted to cargo, life support and engineering systems, not to mention the shuttlepod launch bay and associated systems which occupied a fair amount of space in the lower part of the saucer.