Toronto police were investigating a much bigger criminal organization when they came upon Ford's criminal behaviour. This led to them investigating Ford separately that led to Lisi's arrest in connection with dealing.. That then led to the media being able to gain access to what the police had put together against Ford so far (as far as they had used it in the request for a warrant).
The point being - the Police are very openly investigating Ford, but arresting him for hanging out with lowlifes and admitting to smoking crack is small potatoes. I'm of the belief (and hope I'm not wrong), that they're after bigger charges. Which means building a solid case, gathering solid evidence, and putting the whole filthy picture together. Hell, just following Ford led them to another dealer.
Ford is a millionaire who can afford good lawyers who will get as much dismissed as possible. So putting him in cuffs on something minor with nothing actionable will see him out the door before he sees a cell, and only make him appear a martyr. A real case has to built.