The answer IMO is no real candidates, plus a broken electoral system. Most people who were elected were either an incumbent, or the chosen heir to an outgoing incumbent. Hell, the Councillor and School Trustee in my ward (Toronto Centre) ran a joint campaign, as they were both the chosen candidates by their predecessors. Combined with the mayoral election for Tory being effectively a coronation, I know a lot of people living in my ward who are normally very politically interested and politically active, who skipped the election because they felt it wasn't worth their time to go vote in something that felt like it had such an obviously pre-determined outcome for every race. Simply, we have made it nearly impossible to run against an incumbent in Toronto (with rare exceptions like Grimes losing, but that isn't common), and people are losing interest in elections that feel like an appointment of the chosen candidate by the establishment. And to be fair, if you look at the wards where there was competition (Ward 3 for example), they largely have better voter turnout than the non-competitive races. We need there to be serious competition in every race if we want voter turnout to go up.
Part of the problem here is we run our elections like we're some small town where the mayoral candidates can knock on everyone's door during the campaign. That simply isn't possible in a city of 3 million people. Even councillors are all responsible for over 100,000 people at this point. Most voters don't know who the candidates are, what they stand for, and somewhat understandably, people aren't generally interested enough to take time to research 31 mayoral candidates, plus council candidates, plus school trustees (and if you don't have kids, how motivated are you gonna be to research several school board trustee platforms?). In contrast, a provincial or federal election gives you 3-4 major options and you have a base idea what they are about due to party affiliation. Our elections require much more work on the part of the voter to stay informed. I had 31 mayoral candidates, 9 council candidates, and 7 trustee candidates IIRC. That's a lot of platforms to look into! Plus without the machine of political parties, it's a lot harder to have the infrastructure to challenge an incumbent. Not sure if political parties are the answer here, but our current system is completely broken in terms of voter engagement, and if we want to improve turnout, we need it to be both more competitive, and more accessible to the average person, not just us politics nerds on the internet. Otherwise people will continue to do one of two things, vote for the incumbent cus it's easier, or stay home.