Can't explain it yet. Will have to think the next 17 years about it.

In the meantime, I use uBlock and this custom filter rule to make plain again whatever web designers create or become:

com,org,net,edu,info,ai,io,google,de,at,uk##body,p,li,.text,.commtext,div.u-gap-small:style(font-size:16px !important; font-family:sans-serif !important; font-weight:400 !important; line-height:23px !important)