It's massively successful in the entry level web coding world due to a combination of good marketing and the belief that it gives you unlimited scale 'for free'

It's massively successful in the entry level web coding world due to a combination of good marketing and the belief that it gives you unlimited scale 'for free' and everything 'just works.' Not saying those are impossible goals but so far no database has managed to deliver that. Building a large-scale endlessly-scalable database is still very hard and very detailed and easy to screw up.