If familiarity mattered that much, why wasn't HTML itself replaced by something with curly braces, or CSS by something procedural?
Because HTML wasn't a programming language.
Template languages were like that (e.g. SGML) and worse.
Besides, unlike JavaScript it wasn't the product of a single vendor, but a standard, and the basis upon which the web stood from the beginning.
If Eich indeed had produced a scheme, then it would have been superseded and replaced by another algol-derived language by browser makers soon -- and users would have flocked to that.