You may have noticed by now that the Islefolk strongly dislike animals.
The beasts of Haven are extraordinary in many fashions. They're amazingly resilient, cunning, adaptive and fecund, well suited to their dangerous eldritch homeland, and the vast majority are found only in Haven. However, they require a staggering amount of food- restricting them largely to Haven, where all things of blood and sap grow impossibly swiftly- and, most bewilderingly, they just seem to… hate people.
If human cities were regularly assaulted by wave upon wave of the beasts of sky and land and sea, who tried to tear down our walls and devour our children, I imagine we too would despise the creatures.
The Islefolk believe that not only are animals lesser to people, but they don't really have free will. They are utterly dominated by their hateful instincts, and whatever action they take is solely decided by a set of internal 'programming', to which devouring them is a large part of. To such an end, where it would be abhorrent to enslave or sacrifice people, it is not only fine but quite impressive to manage the same with animals.
In short, Geln would rather not try horse riding for now.
However… the perceptive amongst you will recall that the Islefolk do keep animals! Most of their ships are never meant to leave their waters, and are powered by magnificent sea giants; selectively bred for generations, hand raised from spawning and beloved by their crew; the Islefolk adopt birds and dogs and sometimes even import a horse, and enslave the striding creatures to pull their chariots and serve as arrow fodder when they must. And it is true, the last category is treated utterly abhorrently, with whips and drugs and fire and chains, but all the others are treated quite comfortably.
Amongst beastmasters, the foremost scholars of the topic, there us a strong internal schism between those who like and befriend animals, like Draugnir the Kind, and those who still dislike them but are skilled in breaking them. They expend vial after vial of ink arguing their points, and constantly compete to prove their methods are superior… and have been for centuries, now.
But most Islefolk aren't prone to deep philosophy, and go about their lives without ever questioning this contradiction. They make flower crowns for their sea beasts on festivals and purchase warm nests for their birds, and in the same breath celebrate that they have hunted the great Leviathans to extinction, so no more can they breach their walls. They will trust their dogs to play with children, but will shamelessly assure you that all the other sorts are fit only for the spear and knife, not to be otherwise approached….
If Geln was asked, he would admit that Korra was not as valuable as a random stranger's life. After all… she is still only a beast, a working dog, a mindless extension of her master.
Whether he would actually do as such remains to be seen.