Given that Diogenes was much more disruptive in his attempts to spread philosophy, is there any reason he wasn't sentenced as Socrates was?
I would suggest it is because he didn't have active followers in large numbers until after his death.
Aristotle was subject to the same charge as Socrates at the end of his life, though he was exiled rather than killed. So the degree of disruption, the intention to be disruptive, and the actual hostility evident all seem less important in this particular charge than the number of people affected.
(Although by some accounts, Aristotle's sentence was all about racism and revenge. Aristotle's father was Medean in origin and Athens had gone to war against Alexander the Great -- Aristotle's family's king and his own prior student.)
Athens had very active courts, but no written laws. In the spirit of absolute democracy, elected jurors voted on everything and their decisions were bound by no precedent. So the number of people who directly met the offending opinions and were offended probably controlled whether your case went forward toward prosecution more than any specific definition of the crime involved.
To add to jobermark's answer, it has at least in part to do with the historical context: the Peloponnesian War had ended only a few years earlier, and Athens had just resumed a democratic form of government after the reign of the Thirty Tyrants. Disruption of Athenian society was not a theoretical concern, and so was taken very seriously. Philip and Alexander, on the other hand, did not need to have the same concern for Diogenes.