In the old days, MySQL didn't support foreign key indices, so the LAMP developer community had this mentality that "Joins are slow" or even "Joins are evil" and

In the old days, MySQL didn't support foreign key indices, so the LAMP developer community had this mentality that "Joins are slow" or even "Joins are evil" and actively encouraged people not to use them. So its not really surprising this kind of thing is still out there - PHP tutorials are somewhat infamous for promoting 'worst practices'.