Hello Ragnarök fans and welcome to another chapter of The Ragnarök Theorist, the series that explores the lore of the Ragnarök compilation as a weblog because the author is too inexperienced to do all that hokey video editing stuff to make episodes on YouTube.
Anyways, on with the "show"!
One thing I'm sure a lot of Ragnarok Online players have noticed at least once is that there are absolutely no living horses in the game. None, zip, nada! The only horses we ever encounter are those that are already dead, namely Nightmare, Nightmare Terror, Knight of Abyss, and Lord of Death. Given how Sleipnir exists within the mythos of the Ragnarök compilation, there should be some living horses for players to encounter while exploring the world of Midgard. So what gives? It's not like GRAVITY is incapable of creating horse sprites with the existence of the aforementioned steeds.
According to Old Glastheim, horses did exist at one point in Midgard's history, at least until Schmitz Von Walter's reign in Rune-Midgarts. The White Knightage of Glastheim's Chivalry exclusively used horses as mounts instead of Pecopecos. Sometime between the end of Schmitz's reign to the current era of RO, horses became extinct and Pecopecos became the mount of choice for Knights and Crusaders (until they later transitioned to dragons and gryphons, which is QUITE the upgrade). No wonder horses were not missed very much with all the great riding alternatives out there.
But wait, ZeroTigress! What if horses simply fell out of favor with the Prontera Chivalry?
If Pecopecos became the preferred mount over horses, then there should still be some wild horses around in the modern day of RO. But simply put, there isn't. All the horses encountered are dead (or undead, if you want to be specific). In addition, surely there would be someone who still preferred horses over Pecopecos, but there aren't anyone who still rides horses. If there are no horses around to even have that choice, then the only logical explanation is that horses went extinct and Pecopecos became the main viable alternative.
But hey, that's just a theory. A Ragnarök theory!
Thanks for reading!