I think that you can classify the whole "bike network" idea around Burlington as a work in progress. Assuming that by "bike network" you are referring to the Burlington/Lake Champlain bike path. You probably guessed that it started out as a rails to trail path in the late 80's early 90's when there was literally nothing but industrial ruins on the Burlington waterfront. And it has grown over the years in length and amenities like signage at road crossing and bridges. The City of Burlington and the state funds a lot of the work along with local organizations that help out as well. The iron bridge over the Winooski to Colchester was major money for a bike path. The work on the causeway in Mallets Bay was major money as well. But, I don't think that initially there was any inkling to how popular the path would get. There was no master plan initially. It has grown as usage grows and money becomes available. As for Grand Isle, I suspect that once the bike ferry closes for the season the bike path on the island sees bike traffic drop dramatically. And for that reason, it probably is a little less looked after.

And as other people have posted, the real bike network in VT are the roads. County roads with not a lot of traffic and great scenery.