The most basic reason liveaboard diving dominates in the Galápagos is geography: Wolf and Darwin, the two islands most associated with the region's best shark diving, are only reachable by boats designed to stay out for days at a time. A day-trip boat that has to return to a mainland port by evening simply can't reach them, which rules out the destination's signature sites entirely for day divers.
Beyond access, the structure of the day itself is different. A liveaboard schedule isn't built around a single round trip — it allows for multiple dives across a day, including early morning and late afternoon slots that tend to be the best windows for wildlife activity. Day diving, by contrast, is constrained by fixed departure and return times, which limits both how many dives are possible and when they can happen.
There's also a quality-of-experience difference that's easy to underrate: liveaboard vessels function as floating accommodation, with cabins, lounges and dining built in, and carry dedicated dive guides and marine experts for the length of the trip rather than a rotating day-boat crew. Combined with reaching more remote sites, that generally means smaller crowds at any given dive site than at destinations reachable by day boats from a populated coastline.
None of this is about liveaboards being more comfortable for comfort's sake — the practical effect is more dives, at better times of day, at sites day divers can't reach at all, with the flexibility to adjust an itinerary around conditions rather than a fixed round-trip schedule.
Source: adapted from Galápagos Shark Diving's own published article on why a liveaboard is superior to day diving.