I know what the culprit is: American tipping culture.
Seriously. Some (not all, but some) American servers feel less of a need to care about single tables because their bill is smaller and so will the tip.
I get excellent service in fine-dining, white-tablecloth places when I dine alone (and these are restaurants where I am probably the only person dining alone) in London, HK, Doha, Singapore, etc. That's because restaurant staff from most non-U.S. countries don't depend on the generosity of their customers for their day-to-day wages. They are consequently motivated to treat every diner equally, not just focus their time on the ones who look like they might tip more.
