Designers widely call this as approaches to minimal design though highly debatable. In simple this makes the Comtent repo creation easier and job of visual designer simple since he has to take care of only two components in a full viewport as opposed to loads of content in usual approach. All that has to be taken care is the proper contrast with text against background. Visual designers challenge is when the bg image is dynamic for aesthetics or demography targeting purposes. Bulrring the image behind a bit and or adding a transparent contrasting background as placeholder to text does the job for handling dynamic image.
From full-cycle UX point of view image conveys lots of meaning provided the basic physiological rules are taken care of like; choosing image based on demography; chop the direct eye contact since it is natutal response to look at the eye and the content loses importance, etc. Users do not have time to read all the content so provide short crisp content and aid with not-disturbing bg image. This puts lesser mental load to conceive the content. Plus the page will not bland but colourful or interesting based on the bg. This improves user engagement model.
Generally when you have wide demographic audience, unless the image is properly choosen this will make more harm than good. E.g: When I apply for international unviersity I would like to see students from my country/my race of people rather showing students of different race where the university is located. This brings trust rather just using image for aesthetics purposes or restricted just to local targeting.
