Because the city needs to hold on to its assets (PGW and the airport) until and unless we are in dire straits.
UIL had been running hundreds and hundreds of ads over the summer on the top stations pushing for the sale and basically assuming that it was a done deal. The ads were light and cheery as they introduced themselves to the city and started measuring the drapes. But when City Council began to balk in September, the ads suddenly shifted and took on a dramatically apocalyptic tone - threatening that the streets in the city would start blowing up beneath our feet unless they were brought in to save us.
PGW has been in existence as a city-owned and city-operated utility since 1836, meaning 178 years. For some fly-by-night unregulated energy "holding" company to come in believing the bullshit from our DLC mayor - well, they got a taste of Philly politics. As it is, they would have a hard time operating in a state that still more strongly regulates utilities. And the total number of employees who work for PGW (all municipal employees) is almost as much as the entire workforce of all of the utilities that this holding company owns in New England.
Bravo to City Council!