I suspect MySQL is used with more bare bones schemas, without as many SQL function and complex triggers, as it has worse support for those (IMO, as someone that used MySQL). This does have the side effect of making it very ORM friendly, and the more you rely on an ORM the less you care or even know what queries are being run under the covers.
I've seen this cause MySQL query authors to use various workarounds that end up impacting the query performance negatively.