Lots of ribbons are not that specific, like they might say the show name but not the year so they are able to be reused the next year or if that facility hosts a whole series of shows they can be used at the next show.
Sometimes prizes are donated. Donated prizes and not having to pay for the ribbon would be a win for the show.
Another reason to do this is simply that people do sometimes attend a certain show because they like the prizes, and taking home a prize instead of a ribbon is appealing to many.