I don't know any way to answer this except through speculation, but I thought I might also direct you to some other amazing blind keyboard musicians throughout the centuries.

In the 20th century, we have Monsieur Jean Langlais, who was an organist and a pretty damned good composer of contemporary organ music. His tonalities can be a bit disconcerting if you have a lot of preconceived notions about tonality, but I find his music quite beautiful and meditative.

Jumping back to the 16th century in Spain, we have Antonio de Cabezon, whom we know as one of the earliest composers of keyboard music. His greatest hits include "Diferencias sobre el canto llano del caballero", a lovely performance with historically appropriate ornamentation can be found here.

Now travelling forwards again, we have Louis Vierne in France again during the romantic period. I honestly don't much care for the romantic period for the most part, particularly not organ music, but Vierne was incredibly influential and his music is played today by everyone who studies classical organ ever.

So, blind musicians are certainly a thing. One doesn't really need to see ones instrument to play it--I play with my eyes shut frequently. The notes are always in the same place--it's just a matter of hitting them at the right times.

Several reasons:

The first and most obvious is that music is about sound, not sight, so being blind is not really a disadvantage.

Secondly, playing an instrument rarely involves looking at it. When you've mastered playing it, it is done by feel, not sight. So being blind is a smaller disadvantage (obviously there are situations when being able to see is useful).

Thirdly, it is possible to play (and compose) music entirely by memory. This is tough though. Most people don't have musical memories accurate enough to let them work completely without sheet music. It also makes learning new music much more time consuming, and definitely rules our being a session or gig musician (most non-famous musicians bread and butter) since those require being able to read music on the spot.