JSX & React were literally built to solve Facebook's maintainability concerns, which is one of the most complex client side web apps I can think of. JSX was a hard sell at first 4 years ago, but Pete Hunt did a great job then, explaining how the false separation of concerns between HTML and JS really is unavoidable. You end up with logic in HTML tightly coupled to your JS no matter which way you shake it. https://www.youtube.com/watch?v=DgVS-zXgMTk

And HTML string template languages have been shown to have numerous shortcomings at scale.