It's no ta coincidence an example;
1) Squarespace has much cleaner code and has shcema markup built within automatical, WP not.
2) Second here, wp when you use only 5 plugins wow, thats really great most people have much more! But the catch is , all plugins are messing with your code which is not good for your seo. Least; wp has a database based on old tech very old and slow, SS not, they use coackroachDB a modern , fast world-class DB and cdn.
FSE themes, edit yout templates to make them work when it will work.......then all your plugins messing with your code, so what do you expect in view of seo with all this ?
So you say the majority in internet uses WP, so now what? Does it means you should follow the mass, the herd? Listen, big influencers like Seth Godin, Tim Ferriss and many others, some media news papers , they use the wordpress.com VIP plan, not the standard selfhost wp ,which is a difference like day and night (ok, they have the same weird not working FSE template errors).
WP is dying I see, outdated, a corrupt files, complicated cms it is now , old tech, with FSE templates most times it not works to show you that FSE layout on your specific page.
So when you take a different look in seo serps analyzing on other big sites/ influencers, then you will see that most of them not using selfhost wp, they have different cms like webflow, or wordpress.com VIP plan and others, they have a coder/designer to build their site and they have much cleaner code as you.
That the majority of us people using wp selfhost is not looks like what you think.