It think it's more than young people voting with their feet. I think what you're seeing is the impact of vacancy taxes in metro Vancouver and metro Toronto "working their way through the system". Not only are the reporting requirements (in some cases to three levels of government and to your condo board/management company) onerous, the additional taxes paid on vacant units can get quite punitive for most investors.
In Vancouver the municipal vacancy tax is 3% with an additional 3% levied by the province (plus the feds potential imposition of their underused housing tax). The trigger is 6 months in any calendar year unoccupied and that would include any time needed to renovate and/or re-lease.a vacant unit. For the average $725,000 condo, that could represent in excess of $43,500 per annum or $3,625 per month in annual holding costs. With average rents of $2,500 per month for a one bedroom and $3,500 per month for a two bedroom unit, it takes a long time to recover that (if ever) vs taking a lower rent.