It would be easier, sure, but it would also be unfair. Not all discrimination is harmful, and the state has no business sticking its nose in non-harmful discrimination.
More important than frequency, I think, are these two considerations.
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Is it a necessity, or a luxury? People need food and clothing and housing, so providers of such things should be required to treat all comers equally. But nobody needs diamond rings. If the local jeweler wants to ban blacks from his store, I see no reason for the law to be involved.
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Is it an object, or a service? Selling an object does not imply you agree with the person to whom you sell. But if you personally provide a service, you are making the implicit statement that you think it’s a good thing that the service is being performed. Nobody should be obligated to make such a declaration against his will.