What alternative language do you propose? Not that asking for a source is unreasonable, but you seem to doubt that PHP has majority market share. Do you suppose that Node is more popular? Rails? Go? Flask?
Surveys generally indicate that of sites where it is possible to determine the language, somewhere between 70% and 80% of them are running PHP. Of course, that figure will include a lot of WordPress sites.
What percentage of websites is it possible to determine the language? My guess is not many. Your metric self-selects for recognizing PHP sites because of Wordpress.
