Simplicity to me entails knowing the difference between a need and a want.
You can have tons of stuff materially and be completely miserable, because you feel as if you need to continue accumulating "stuff".
You can have just the bare necessities and be content, because you recognize that you actually do have everything you truly need.
It seems to be a state of mind, and perhaps it's even a decision that a person makes to the effect that "As long as I have food, clothing and shelter for my family and me, that's all that really matters."
We certainly make our lives more complicated, and our society's throw-away mentality has contributed to it enormously. If something doesn't work, you toss it and get a new one. Don't be bothered to try and fix something, because it's cheaper to just toss it and buy a new / better one. Don't try to learn how to fix something because time is valuable, and by the time you fix xyz yourself, you could have earned twice as much money in the same amount of time. The take home message is that "stuff" is important, but knowledge, experience and learning self-sufficiency is not important.
Sure it takes time and patience to grow my own tomatoes and zucchini and beans. Sure it takes time to make my own bread instead of picking up a loaf at the store. Sure it takes longer to make a trip to the egg farmer to buy fresh locally produced eggs, or buy produce at the farmer's market, than to walk 600 m to the grocery store and buy eggs and produce from who-knows-where for $2/dozen. Sure it takes time to paint a room myself instead of hiring someone to do it for me. Sure it takes time to knit a pair of socks instead of buying the generic ones in the store. Sure it takes time to clean my own house instead of hiring a housekeeper. But doing those things forces me to change my priorities - unlike some of my friends, I'm not focussed on social events or gossip and other drama that seems to occur in people who actively seek out the complexities (ie, the drama) and thrive on it. Oddly enough, they always seem to be miserable...