I suspect, I repeat suspect, that security in the airport is contracted out to some private sector company. That company may or may not have gotten fucked during Covid when GTAA told them that due to reduced volumes, they didn't need so many staff. So they laid them off. It could be that the company provides staff as requested by the GTAA. All well and good when it's situation normal.
But when they laid off half their people, it became impossible to get them back a year and a half later (and who could blame the staff for finding other jobs).
Now they can't find people period, and certainly not at the wage they were paying pre covid.
Now here's the part in almost sure of....
Said private company has gone to the GTAA and said, we need to attract more people by paying a higher salary (which is true) and Mr. GTAA you need to pay more. (Now how do you think that went over with the GTAA?). That's right, the GTAA has told said contractor, "that's your problem, read your contract"
I'm guessing again that the security folks at YYZ aren't making that great of a salary. (I have no idea how much they make, but Im going to guess very low 20s an hour.). They probably need to pay 30 an hour now to attract people. But the GTAA won't pay a dime more other than what is specified in the contract so the short staffing will continue.
The only solution I see is that the GTAA cracks and pays them more to attract more people and tacks the cost on to the fees they charge airlines. I will certainly pay 20 bucks more a flight if it means I don't have to sit in the airport for 4 hours.
If I've learned one thing over the years, it's that money cures all problems.