HTML5 was born in an era of decent HTML authoring tooling. Very few people write HTML by hand nowadays. This was not true of earlier versions.
Also note that HTML5 codified into liberal acceptance some of the "lazy" manual errors that people made in the early days (many of which were strictly and noisily rejected in XHTML, for example).
Also note that HTML5 codified into liberal acceptance some of the "lazy" manual errors that people made in the early days (many of which were strictly and noisily rejected in XHTML, for example).