I think you've missed something there. Your point about prejudice is quite valid, but that prejudice was actually an asset for Susan.

Many, many people, a LOT of people, can sing. It is not at all an unusual talent for humans.

What makes a singer popular is something else added. They need to be unusual in some way. Unusually pretty, sexy, funny, personable, witty, strange, weird - something has to make them stand out from all the millions of others who sing just as well. A bland, colorless, uninteresting person with great singing ability will be handicapped in a contest like that.

Something has to make them memorable, something has to create the buzz. Susan had that, but a dozen more like her would not fare as well because they would not be unusual.