You’ve highlighted the main problem - the brides get compared. And it’s not a nice feeling for the other bride(s) who may not look as good for whatever reason. I guess it works out cheaper so there’s less of a burden on the parents, but it’s still better that all of this is avoided.
This may sound a bit selfish, but it’s a once in a lifetime day for the bride, and she should be able to shine without having to share the spotlight.