But PHP has a legacy, lots of bad PHP code exists already, bad practices are usually the first result on google and very "lazy" developers who never learned anything else exist and this muddies the waters very much when talking to people who prefer to build new things in PHP.
There's also the nitpicky fact that the old way of running PHP was that every page request runs the code from scratch, meaning you have to build state each time which is profoundly expensive and inefficient, although I believe people rarely do this anymore it's still definitely the default for most PHP projects I've seen. (both FOSS and proprietary).
I don't like your overgeneralisation about junior/mid/senior developers, the lines are super blurred in the real world. (I say this as a non-developer who works with developers)