I don't know why. It didn't make any sense to me either. The statement "I needed to keep above 250% FPL to stay out of Medicaid range" was my personal experience. That's why I stated it that way, rather than in a general way. To shed more light on my experience...I went through the sign-up process on the federal exchange many, many, MANY times, only to get "snagged" by Medicaid. There's supposed to be a breakpoint at various places, including 230%, I think. I tried them all. And the only way I could keep my family and I out of Medicaid range was to go above 250%.
Folks like to point out how awesome a silver plan with cost sharing is. For me, though, cost sharing doesn't do much since the three of us might have a total of four or five doctor visits a year. Even if these visits were 100% free, that doesn't make up the difference between the cost of a Bronze plan and a Silver. That's not to say I won't revisit the analysis every enrollment period! Basically I'm buying the max out of pocket, and the negotiated rates, and I know that's not true for many that use more health care services.
I think what makes it confusing to talk about is that in different states, with different health insurance needs, there are so many variables that generalization can be problematic.