As with every trend - at some point it becomes cliché, and doesn't taste fresh.
In this case I think there are two basic reasons why "Make It Big" trend continues (and probably will continue) to be popular:
Having 100% of the screen at the designers disposal helps to create "visual impact" - whether this impact is good or bad depends upon the quality of the designer and the personal taste/preference of the recipient.
This type of layout almost always works in each resolution without having to put much work in fine tuning resolution depending on design versions. Implementing (I mean basically writing CSS) these designs is a breeze when compared to more complex layouts that need exceptional amount of work and CSS expertise to assure fine result in all devices.
Using or not using this concept is IMO a matter of application.
Agencies strive to make a "visual impression" in agreement with the famous quote "A picture is worth a thousand words". It certainly doesn't excuse the lack of imagination in overall concept of a brand or putting the "instantly forgettable line" on the frontpage.