Underage Servers

I went to a newly opened village pub tonight. It employed a teenage waitress, who was prohibited by law from delivering alcohol to tables, or even to put alcohol orders on the same ticket as the food. The alcohol was to be brought to the table and rung up by the adult owner of the pub.

To people who write these laws: who do you think you're helping?

What purpose does this serve?

Yes, it does seem hypocritical to allow people who aren't old to drink to serve what they can't consume.

But is it really?

It appears to me that it just hurts the efficiency and quality of service of the pub.

After all, pharmacists are allowed to sell prescription drugs that they themselves are prohibited from consuming without a prescription.

How is this different?