Why proprietary template engines are used instead of html5?

Question

All the popular frontend frameworks(angular, ember, react etc) use proprietary template engines. I'm wondering why a proprietary template syntax is used instead the standard html5 <template/> tag. Is there a technical reason?

Answer 1

They're different beasts: template engines do a lot more than hold HTML for filling in later.

They include loop control, conditionals, various ways of implementing EL engines, and so on.

That's out of the scope of the tag to my understanding (which is limited and possibly wrong).

In addition, template engine designers have a lot of different... ahem ... views regarding what should or should not be the responsibility/functionality of a template, which is one reason there are eighteen million of them.