Can understand why they want to seat 4 at a table instead of one..however its really stupid to turn your locals, that you depend on 80% of the year, against you, to maximize money from tourists who are there only briefly.

Which is exactly what they are doing, cause those turned away solo diners? They'll tell their friends. and a lot of them wont go to those restaurants anymore, solo or in groups.

Bet that tourist money wont be enough to carry them through the year till next tourist season, bet a lot of restaurants that do this close.

This is the best summary I could come up with:

Local people are becoming increasingly frustrated by restaurants looking to maximise profits from tourists during the busy summer season.

But it's bad news for solo diners as restauranteurs have started turning them away in favour of groups that bring in more money.

In central Barcelona, some restaurants - mainly on Carrer de Blai which is known for its tapas bars and in the Eixample neighbourhood - have started turning single diners away.

Spanish daily newspaper El Pais reported that waiters are giving excuses like being fully booked or refusing seats on restaurant terraces.

As temperatures start to rise in spring, residents are forced to adapt to the eating schedules of tourists, with many establishments refusing to accommodate those looking for a quick drink after 12 pm.

Before entering the MACBA (Museum of Contemporary Art Barcelona) we want to have a coffee,” journalist Noemí Vilaseca said in a post on social media in July.

I'm a bot and I'm open source!

Really, this means your restaurant should have a counter or bar where you can seat solo diners without idling 1-3 table chairs.