Speculating on what could have motivated this, entities that are valid without ";" as per https://html.spec.whatwg.org/multipage/named-characters.html appear to be mostly those with Unicode values below U+0100, i.e. roughly the original Latin-1 set.

This is probably due to the fact that old versions of Netscape always accepted some of these forms, but that this should only be considered as backwards compatibility to pages written for older browsers with limited character sets (e.g. "&degC" rendering as "°C"), but not something to proliferate for the rest of Unicode.