I don't have the direct experience you do, but when you say "training and support" I would venture that includes "the vibe" of the thing.
People who have used Windows & Office forever will find using a new platform irritating just because everything is just a little different.
Couple that with the fact that non-tech people often perceive opensource as the free+shitty version, and it's surely a recipe for an "ideology" whereby employees feel that they're being abused - forced to use a shitty platform so the city can save a few dollars.
There's also a halo effect, whereby any issue gets blamed on free+shitty platform instead of simply tech being tech.
I just don't think that training and support can really solve that. You really need employees to believe in the benefits if opensource and I'm not sure that's achievable.