The following description of the reasons for the Kelly outbreak comes from the report of the Royal Commission. There are many other reasons. It depends upon your point of view. What do you think the KellyGang would have thought.
"In the opinion of your Commissioners,
the abolition of the Glenmore station,
the reduction of the numerical strength of the force in the district, and
the substitution of inexperienced and inferior constables for those more competent, necessarily weakened that effective and complete police surveillance without which the criminal classes in all countries become more and more restive and defiant of the authorities.
The incident, however, which seems to have more immediately precipitated the outbreak was the attempt of Constable Fitzpatrick to arrest Dan Kelly, at his mother's hut, on the 15th of April 1878.(RC181) (RC13340)
Hare's view, see (FH)
Const Flood suggested, 'Well, my impression is that it was the removal of a number of old constables from the district who knew the district well, and the taking of men to the district that did not know the district well.' (RC12617)
This was supported by Graves from Kilfera and the member for Delatite. The said, 'It was in consequence of sending men who were inefficient as far as the country was concerned, that the Kellys got ahead' (RC15493)
It may also be mentioned that the charge of persecution of the Kelly family by the members of the police force has been frequently urged in extenuation of the crimes of the outlaws; but, after careful examination, your Commissioners have arrived at the conclusion that the police, in their dealings with the Kellys and their relations, were simply desirous of discharging their duty conscientiously; and that no evidence has been adduced to support the allegation that either the outlaws or their friends were subjected to persecution or unnecessary annoyance at the bands of the police." (RC2nd reportIII)
The economic reason is well set in long article (Argus19/4/80)
Insp Montfort's assessment;
From information I have received, I do not think there is any cause to fear a similar outbreak except under certain circumstances. I have received private information that there are perhaps half-a-dozen young men who are closely connected with the late gang who would with great satisfaction rally round any men who, by the commission of any crime, might bolt from justice, and whom they considered competent to lead them. That, I believe, is quite on the cards at present. (RCApp1) See also (The Age 4/5/1881) (RC3561)
After Glenrowan the police tried to find out more information about the KellyGang but they had little joy because there was no money to pay for it. (RC2961)