With Gen. Flynn's plea to lying in testimony, the likelihood is that he would have pleaded to more if this was going to move any further. It is likely this was the most Meuller's DNC-donor-heavy partisan hit squad has pushed this investigation as far as it will go. And to do so, Meuller took the Special Investigation (set up to investigate the Trump campaign's alleged illegal/treasonous "collusion" with Russia prior to the election) >>>FAR<<< outside the scope of what it was created to investigate.
With Flynn, it convicted him for doing things that were legal when he did them, but for which he lied in testimony about what he was legally allowed to do. It is normal for an incoming elected administration (between the Nov 5 2016 election, and the Jan 20 2017 inauguration) to reach out and establish relationships with foreign governments with their "transition team"), but for some reason Flynn did not want to disclose what he had legally done, and lied. Flynn's only real crime was not disclosing that he had prior to joining the Trump team, acted as an undisclosed representative in other matters for the Turkish government.
The lead investigator for Judicial Watch (on Lou Dobbs Tonight yesterday, Dec 1 2017) said "give me two hours of deposition with anyone, and I can make them lie in testimony." There is no crime, just someone who didn't know how to legally answer the question.