Morkus from Orkus
No. The simplest explanation is that since D&D Beyond's free character builder only gives you one choice, Champion, everyone who wants to play a fighter and not pay for the service is picking......................Champion. WotC and DDB are skewing the stats and then presenting them as "popular" when the reality is that there just isn't any other choice unless you want to pay $$$.Unless you think wotc and DDB are lying about the stats, there isn’t any reason to demand more in depth analysis before being able to talk about what the stats can tell us.
There is no reason to think that a bunch of ridiculous nonsense is happening to make base human champion fighter reliably the most common choice. The simplest explanation is that people like those options, more players want simple characters than any other individual specific desired character type, and the Champion is the basic iconic fighter.