Why is this a problem? Reuse is incredibly important for building almost anything on the web, and it's been with us since long before the web platform supported it natively, e.g. with CGI scripts that used Perl functions, to output repeated HTML "components", or PHP, web frameworks, etc.
If you don't have some method of reuse in the platform or framework, developers either have to copy-and-paste (and deal with so many difficulties of updating and maintaining consistency that it's not a realistic option), or push reuse to a non-standard layer of the system like server templating.
Server templating is fine, but it doesn't actually get rid of the implicit concept of components that'll be in the page or app, it just disaggregates it among to non-colocated parts of the system.