Why would he?
(a) He was dealing with a journey which would last months, not millennia
(b) He was proposing a route to find and bring back spices to Spain without having to go through Portuguese waters => there was an economic benefit to his journey, which isn't the case in the research and invention of a new propulsion system which would cut the distance to the nearest star to a mere 5000 years.
(c) Most of his crew were convicts, so nobody cared about them, and I'd say they were paid very little and
(d) Three boats (already invented) cost a lot less than an intergalactic spaceship (not invented)
It's like saying a two inch wall is as easy to get over as a two mile high wall - both are similar problems (there's a wall in your way), but one's a hell of a lot easier to get around (or over, in this case).
As GavinZac noted, America was already discovered. St Brendan sailed there from Kerry in the 6th century. He wasn't the first to do so either - he just wrote a book about it. Leif Eriksson (Erik the Red) sailed there from Norway in the 11th century. When they got there, they found people (as did Columbus). They'd crossed a land or ice bridge from eastern Russia to Alaska and into Canada. America was discovered in the 15th century. Just, like lots of things, people had forgotten about it.
And in any case, your point again has no relevance to the point at hand.