Taking care of elderly parents -> you probably should get more money
Health problem in the US -> you probably should get more money
Crippling mortgage. This one depends a bit. Does your job require you to work at a specific location, and the location has a high cost of living. Then yes, you should get more money.
Think of the "no dependents and responsibilities" as the base rate. And you get extra depending on your needs (as listed above).
If you think this really crazy, consider that in the US, all of these things are tax deductible. Which means that its already normalized for people with such needs get more money (in the sense of more after-tax money). So why would getting a salary bonus be so wrong?
Or at least that it should affect what your employer gives you.
It's straight up discrimination, and some of it (e.g. based on parental status) usually illegal.
Taking care of the sick, elderly, and children is a social issue, and belongs with the state. Not by illegal arbitrary discrimination.
Also imagine how humiliating it would be for someone failing to conceive to see insult to injury that they don't get a bonus but their team mate does.
Paying someone less for doing more work (i.e. not picking up from daycare) is incredibly disrespectful and demotivating.
I hear all the time that someone asks for more money because they just got a new house. Like... What? Your employer is now responsible for you choosing to live beyond your means?
In both scenarios we put ourselves in that position.
Maybe I have a health problem, and live in the US.
Maybe I'm taking care of aging parents.
Maybe I have a crippling mortgage. Too big a house. Live downtown, etc… etc…
"You have no dependents and responsibilities so I'll pay you less" is basically age discrimination in addition to discrimination based on parental status. Both often illegal, and for good reason.