By installing a small extension on your browser (eg Wappalyzer) you can know the technologies used behind each site. I use it daily to find out what is used on the latest award-winning Awwwards sites. As you may know, it rewards every day a site that has illustrated itself for its design, its user experience, its animations or its innovations. It is clear that WordPress is very often represented. Despite a reputation not always at the top WordPress remains a very good CMS to make a very good graphic site for 3 reasons:

• The cost: WordPress is easy to set up, to apprehend and the community is immense. It is therefore easy and fast to set up to focus on the essentials: the front. Moreover it has the advantage of being maintainable since it is known to a good part of the developers.
• The ergonomics of the back office. Unlike many competitors its use is very easily apprehendable by customers. This is sober, there are not many options and there is a plethora of textbooks and other tutorials to know how to use it.
• JSON Rest API. It is a plugin that allows to export all the contents of its site in the Json format. You can use these contents on the front-office in javascript in a completely independent way. It is this technique that is mostly used by agencies in addition to a javascript framework like React, Backbone or Angular.