The bags are put on by whoever installs the tree, generally, which may be the City, but is often a private contractor (the City contracts out a lot of tree planting).I have never once seen the city fill up these water bags! They went on a blitz installing them but never filled them up unlike other jurisdictions. Got to wonder how much they costed the city before they were removed.
I believe the watering is in the tender conditions, but I can't be sure.
I know with contract tree planting the tenders have a 2-year warranty on the trees which the City can enforce is the tree is dead in under 2 years from planting.
But it would not surprise me if watering wasn't followed up on and replacement trees looked at as a cost of doing business.
Filling water bags for thousands of trees is really an expensive enterprise.
Treegator backs typically require filling once per week in warm weather.
That's one full water truck for 400-800 trees.
Its a very expensive prospect.
I don't recall Parks having any full sized ones in their equipment pool; but I could be wrong. Though I'm quite the City has 1 or 2 buried somewhere.