I think it took this long because of the litigious society we live in.
Before they could legalize it, the govt had to address stuff like driving stoned, smoking pot in the workplace (or at least in the outdoor "cigarette" areas, who is willing to bribe the politicians for favourable decisions, taxation, legal age for buyers, and other points that nobody cares about until someone is "infringed upon."
For years in Toronto, the police haven't cared if you walk past them smoking a joint. The only charges have been laid against the businesses that were openly selling. And that's really only because they were flaunting the fact that they were still breaking the law. I doubt any sidewalk dealers have been charged in years.
It's finally becoming legal in Ontario. I haven't smoked pot in 20 years, but am glad to see that the incredible waste due to prosecution is coming to an end.