The same reason you couldn't in 1996: because the assumed entry point for the language is someone who can barely conceptually manage HTML; doesn't want to have to deal mentally with the fact that numbers and text are fundamentally different kinds of thing; and - most importantly - absolutely will not accept the page failing to render correctly, or the user being shown an error message from the browser, for any reason that the browser could even vaguely plausibly patch around (just like how the browser has to guess whether an unescaped random stray < is just an unescaped less-than symbol or the start of an unclosed tag, or guess where the ends of unclosed tags should be, or do something sensible about constructs like <foo><bar></foo></bar>, or....)
The same reason you couldn't in 1996: because the assumed entry point for the language is someone who can barely conceptually manage HTML; doesn't want to have to deal mentally with the fact that numbers and text are fundamentally different kinds of thing; and - most importantly - absolutely will not accept the page failing to render correctly, or the user being shown an error message from the browser, for any reason that the browser could even vaguely plausibly patch around (just like how the browser has to guess whether an unescaped random stray < is just an unescaped less-than symbol or the start of an unclosed tag, or guess where the ends of unclosed tags should be, or do something sensible about constructs like <foo><bar></foo></bar>, or....)