Guess what, you're not required to open <html>, <head>, or <body> either. It all follows from SGML tag inference rules, and the rules aren't that difficult to understand. What makes them appear magical is WHATWG's verbose ad-hoc parsing algorithm presentation explicitly listing eg. elements that close their parents originally captured from SGML but having become unmaintained as new elements were added. This already started to happen in the very first revision after Ian Hickson's initial procedural HTML parsing description ([1]).
I'd also wish people would stop calling every element-specific behavior HTML parsers do "liberal and tag-soup"-like. Yes WHATWG HTML does define error recovery rules, and HTML had introduced historic blunders to accomodate inline CSS and inline JS, but almost always what's being complained about are just SGML empty elements (aka HTML void elements) or tag omission (as described above) by folks not doing their homework.
I'd also wish people would stop calling every element-specific behavior HTML parsers do "liberal and tag-soup"-like. Yes WHATWG HTML does define error recovery rules, and HTML had introduced historic blunders to accomodate inline CSS and inline JS, but almost always what's being complained about are just SGML empty elements (aka HTML void elements) or tag omission (as described above) by folks not doing their homework.
[1]: https://sgmljs.sgml.net/docs/html5.html#tag-omission (see also XML Prague 2017 proceedings pp. 101ff)