MMM definitely makes most sense for people who enjoy doing the sorts of things MMM enjoys doing. I happen to really like a lot of the around-the-house type DIY projects, so it's a good fit for me, but I don't think there's a moral imperative to it. MMM sets the "$30k/year" bar for frugal family living with his DIY lifestyle, but there are plenty of people who do it differently. My wife's extended family are for the most part recent immigrants, so a lot of them live in that range (comfortably enough!) with a completely different type of frugality.
I actually like doing those sorts of things too. But as my engineering skill-set grows, I also start to really notice the opportunity cost to doing them. You can keep doing them, for awhile, sure. But if you're actually pushing your personal productivity and value flywheel, those costs are going to weigh ever heavier and eventually you're going to have a decision to make. Outsource the things that aren't adding momentum to those who would be happy to take them off your hands or stop gaining momentum. Because as the flywheel gains momentum you have to push ever harder on it to make it go faster.
It doesn't just apply to household stuff. A business has to be able to scale beyond your personal efforts as well. To do so you have to be able to remove yourself from a lot of equations. Large impacts to society and the world don't really happen without institutions, and institutions can't get built any other way.
What I love about engineering is the personal value curve is so steep, that it starts making sense a lot sooner to outsource drudge work. It becomes a question of, how big do you want to grow, and how fast do you want to do it?
