Why? People with "low aspirations" are not necessarily bad people, nor unsuitable mates. Everyone needs something different in their lives. All I'm saying is that "self-improvement for the sake of dating" is terrible advice. Most people want to go on dates with people who are attractive, and self-improvement is often an anti-pattern for that. Yes, we'd like to think that everyone has real standards (versus superficial ones), we'd probably even like to think that we set real, personality standards for ourselves, but that doesn't get you out meeting people, and it can be extremely intimidating when you actually do.
It's merely bad advice because that's not what people are looking for. Even people who might intellectually think "oh, I'm looking for a good guy/good gal" are not six times out of ten (that's a made-up statistic)