`Traditional` [ read old ] web-sites without a framework are not the enemy and coding in `vanilla` PHP | JS is perfectly fine depending on what you are doing and how the site glues together. As you may wish to read, the idea behind MVC is to break up the logic, the data and the presentation of a site so that `different` people can work on different parts of the site.
Obviously this is a good structure and one of the many reasons why people like MVC, but for a lot of sites which just have static pages, i.e views and basic AJAX/jQuery functions to make them nice and dynamic, MVC can be a sledgehammer.
We have plenty of non MVC sites in use and they are working just fine and very interactive with the use of AJAX. We wouldn't start a non MVC site these days, because of new Tech, but if you have a Traditional site and you'd like it re-factored into PHP MVC or a ReactJS framework, then we would be happy to assist you.