Every time I see a new CMS or a trend in CMSs, 'simplicity' is touted as a selling point.
This is a thing because web publishing is inherently complicated and people want to reduce that complexity. Simplicity is also often used synonymously with "faster performance".
For example, a lot of people who promote systems like Jekyll and Kirby will say they are "simpler" compared to WordPress because they don't need a database engine to work.