The threeboot held around 25,000-30,000 so not great but not near cancellation when compared to manhunter and blue beetle which sold in single diget thousand before they were put out of their misery. Legion of 3 Worlds was in the top 30 comic books sold, I'm sure those new readers along with those already familiar with the threeboot would have provided a great foundation for a restart featuring the old legion. But no, DC wants to waste the momentum coming out of the mini on connor kent rather than working through the storylines Johns set up in #5. As it is we are in for months of origin stories and teases about storylines DC could be getting on with.
Remember mysa the black witch? in 3 years when they get around to telling that story no one will care. My faith in DC and the Legion is that low. I don't think Didio 'gets' the Legion.