30 years ago, I managed a Burger King, and even then, they had us send people home if it got really slow, or.. call up people and cancel their shift an hour before, because of bad weather, etc. Someone's already arranged childcare or transportation for their shift, then cancelling it same day is just not a way to work.
I would imagine that a lot of places are still like that today.
$15/hr sounds great, but if it's 20 hrs one week, then 7 the next, then 24, then 4... that's still a bit unstable for a lot of folks. For someone who has no dependents, or has a stable partner... it's probably doable.
Norwegian link: https://www.arbeidstilsynet.no/regelverk/lover/arbeidsmiljol...
So if Norway were having the same issues with employee shortages you could add the reason that maybe the employees are tired of having the company steal from them.
And maybe that's a factor common to other countries
Also, I used to manage a McDonalds. Paying a bonus to have people come in on short notice to cover no-shows, sick calls, or unexpected business volume was not uncommon.
The problem is McDonald's Corporate only owns 5% of McDonald's locations, the rest are franchise locations, thus a "McDonald's" crew member at a non-company store is not working for McDonald's but the Franchisee.. This is where you get the lower wages..
This allows McDonald's to get headlines about offering a "$15 min wage" while 95% of wearing an McDonald's uniform do not work for McDonald's thus do not get this wage
Also, have you seen inflation lately?