I think at the heart it mostly boils down to a combination of greed & laziness, sometimes with the hopes of a legitimate work-at-home job or out of desperation, which is understandable. The line of thinking always seems to be, "If I can just sell this simple product, I'll make it big!" The reality is that it involves people pushing products onto friends & family and having a lot of inventory that you pay for. I know a lot of people who have tried MLM's at least once & finally seen them for what they are, and I currently have two friends who are still completely stuck on them. One sells Monavie (magic fruit juice) & the other sells Doterra essential oils (magic alternative medicinal claims). We've had to stop inviting both to our house...they're so sucked into it that they can't see how ridiculous it has made them. Basically turns you into a scam artist where you believe your own hype. There's just something about MLM's that make people with certain personalities drink the kool-aid.
Not all of them sell bad products, either. Cutco knives are fine. Mary Kay actually has good makeup products. But an awful lot of them are into the pseudo-science side of making medical claims, among other things. MLM's are just so scammy. I don't need people I know trying to sell to me on my personal time. RIP relationship if you do that! I think it is useful for people who get suckered into them to go through the experience at least once, so they can really be exposed to what's going on. And of course, if you're in the top 1% of the MLM, you're making bank in the pyramid scheme...Amway made like ten billion last year.