Why only republican let "voters choose candidate"?

People say "in primary voters dont choose a candidate" but they do!
People say "in primary voters don't choose a candidate" but they do!

1, Why don't democrats do same? Meaning democrat primary "voters chose" philips! So when biden left, philips is the one next, second most voters, if "voters chose" but why not like republican that voters chose?

2, Why no outrage by democrat voters that they didn't choose harris?

Why only republican let "voters choose candidate"?
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