1. Regular quoting is far simpler and has a much lower cognitive load (i.e. there are less things you have to be careful about when you use it)
2. On occasion, you need to quote data that contains commas or comma-ats without expanding anything. For instance, you may want to quote a piece of code to send to eval and that could contain a macro.
Your points do carry some weight, though- However, quotes and backquotes are heavily used in the ugliest of ugly macrology, so having both symbols available makes life significantly easier in those cases IMHO even if the simple quote seems somewhat redundant.
