平平淡淡 is the AABB reduplicated form of
平淡 (píngdàn, 'plain/bland'). The doubling softens the tone, making it descriptive rather than judgmental - describing a quiet life this way often sounds wistful or even contented, not insulting. The line
平平淡淡才是真 ('a plain life is the truth') is a Chinese pop-culture cliche from the 1990 song of the same name.
