Hoping to reach India, as taught to everyone in both Europe and India, Columbus realised the Earth was Flat.
Using genovian maps that could help someone from one location on the Flat Earth to sail in a concentric circle pattern around the earth's center in North Pole Arctic Circle, was a difficult feat then.
Especially if you sought to sail from Europe in an arch like pattern, through the endless ocean, to India more than 180 degrees, or half the distance of the world disc.
For this Columbus required compass to point directly west, without which sailing in a straight line might have thrown him off the World's Edge, far away from both Europe and India.
So sailing around the world's center in the Arctic Sea, was necessary. Making sure their compass wasn't broken, the winds still threw them off course a bit south, I expect. But not enough to throw them into the Ecuatorial Calm, which they knew very well to avoid. For not avoiding it, meant they would be tossed in the Outer World, and thus closer to the World's Edge, and furthest away from India, than before.
Thus Columbus the Flat Earther made sure he would sail course describing a perfect circle around the World's Core, instead of sailing directly ahead, into Antarctica, and hit the World's Edge.
That's why this journey was so feared. They had no way of knowing they would sail perfectly at the same latitude, in a circle, instead of a line, failing to reach India completely.
Spain being in the same Concentric Circle as India, sailing on the Flat Earth, westwards, and ending up on the other side in India, should be perfectly viable. Unless you hit some other continent like America, instead.
If Columbus has simply walked cross America, from east to west, then continued to sail on new built ships, keeping the same latitude, they would have reached India. Assuming they didn't miss course on the vast Pacific.
This is why this was so dangerous and "risque". Having known the Earth is Flat, keeping course perfectly west to hit India, from "beyond the seas", was very difficult. It's like hunting blindfolded, with the barrel of your gun pointed behind you, over your shoulder, and hoping to actually hunt something.
So it was very dangerous. Dying at sea, being lost in the "Okeanos" myth these young europeans still inherited from the Greeks, the myth that Eurasia and Lybia are the only land masses on the Flat Earth, and the rest is 90% vast sea called "Okeanos".
Columbus knowing how hard it would be to keep this west course perfectly until they sailed in a semi circle over 300 degrees around the Core of the Flat Earth, would be most perilous, he was only hired by the most desperate of Kingdoms. The Catholics who were losing trade to the Ottoman horde and barely defeated the Moor pirates, were desperate enough to rekindle their trade with the Orient.
Since sailing around a flat earth would indeed give them this opportunity they bravely took the chance. Only America was in their way, blocking their ships from sailing directly west. Oh well.
The other course was sailing through the Arctic Sea, over Eurasia, but of course most of them died from the cold and lack of supplies or fresh water on this nothern route.
While the route down beneath Africa, close to Edge of the World in Antarctica, then through the Indian Ocean was very slow because it went beyond the capes of very large continents, and requires them to sail through the Southern Seas, which are the largest of all, compared to very small Northern Seas.
So only a middle course was possible, on this Flat Earth they worshipped. Not one too northern to avoid the Arctic cold, not one too southern to fall beneath the Ecuator into the vast Southern seas that neared the Outer Edge, but just right. In the middle, in perfect latitude. As Spain has a comparable latitude to India, sailing directly west in a semi circle to it, was even faster than having to walk east in a semi circle to reach the Orient and India.
Since seas were a lot safer from pirates which thrived in ports of Africa and the Orient, there would have been only clear sailing westwards on Okeanos. Unless another continent halted their advance, which they may have no expected to happen. In this case their path to India would be blocked on the Flat Earth, by another continent.
Enough of your complications. This is FET history and it's the most reasonable of all. Or have you not enjoyed proper European education to understand this ...