Because some jobs are worth something and that something isn’t worth a living wage?
I have to cut my lawn once a week. (Well, I suppose I don’t have to, but the HOA will get angry if I don’t). So, there is some value in doing that job - happy neighbors, lawn looks nice, whatever. Of course, I don’t particularly enjoy mowing the lawn myself - it’s hot and sweaty, I have to remember to crosscut, The curvy bit by the day lilies is a pain to mow and I need to go back with the weedwhacker to fix it. So there’s an opportunity for a job here - I could pay someone to cut my lawn. What’s that worth to me? I’m pretty frugal, the lawn isn’t that big, yadda yadda - maybe it’s worth $10 to me.
So, someone comes by and says “Hey, I’ll mow your lawn for $10”, I could be persuaded to hire him. Someone else comes up and says “Hey, I’ll mow your lawn for $5”, well, guy #2 is getting that job for obvious reasons. But if the only person that shows up says “I’ll only mow your lawn for $15”, then looks like I’m mowing the lawn myself. Guy #3 has priced himself out of a job.
It’s similar to the things people have said previously about automation. If it costs a McD’s owner $20,000 a year to install, maintain, and update an automatic ordering system, and $15,000 a year to hire someone to do that, someone’s getting hired. If that person turns around and says “I’m not working for less than $30,000 - that’s a living wage, and if the work is worth doing, that’s what you should pay” - that person has priced himself out of a job because it’s not worth what he wants to get paid.
This doesn’t just apply to low-skill jobs either. For example, I was at a convention this weekend, and it had an art gallery where some artists had work for sale. Now, oil on canvas is not a skill most people have - in fact, I would be happy claiming that less than 1% of people could paint with the kind of skill that those artists had. But no way in hell am I paying $1500 for a 1 square foot painting. I did, however, get a $35 print that was about the same size.
Now, can an artists live off nothing but $35 paintings? I dunno, that’s not really my business. But if someone comes by and tells me I can’t buy a painting for less than $500 a pop because that’s a “living wage” for an artist - those artists aren’t selling squat. Same with the low-skill worker - some jobs are worth $15 an hour, and some aren’t, and if you force a wage hike, some of those low-skill workers might find they aren’t worth $15/hour after all.
Does this mean the low-skill worker deserves to starve in the streets? No, and I resent the implication I’ve seen from some that saying “this job isn’t worth that pay” translates to “I hate poor people and want them to die” - nothing is further from the truth. But it’s not McD’s responsibility to see that Hubert Hamburger-flipper has enough to live on - that’s all.