Rodents are, generally, regarded as kids' pets. These days, most kids get a hamster as their 'first pet'. In the 1990s, however, the rodent pet market was pretty evenly divided between hamsters, and gerbils.
Gerbils were a fad pet. It happens fairly often - Dalmatians, for instance, were super popular for a brief time after the release of 101 Dalmatians. Soon enough, people realized that the breed was too much for them, and shelters were flooded with Dalmatians. Eventually it evened out and they're back to being the relatively uncommon breed they were before.
Gerbils were very popular in the 90s, as classroom pets and for children. I grew up with gerbils, not hamsters, and I still prefer them. They're smart, active, gentle, social creatures. But for whatever reason, they fell out of favour and most kids have hamsters now. Gerbils have become fairly rare. This means that when we get gerbils at the shelter, it's a nightmare trying to get them adopted - nobody wants a gerbil anymore.
Gerbils are one of those species that take forever to be adopted. Chinchillas take forever, doves take forever, and gerbils take forever. It's just inevitable.
I will never understand why hamsters emerged 'victorious' in the childrens' pet industry. I love my hamsters, but gerbils make better pets. They're awake during the day, they're less likely to bite, they're smarter, they're more active. But - and I do think this worked against them - they have tails. And tails make people think of mice. Hamsters are fluffy and tail-less.
Cute wins over practical every time.