I'm curious, why do people use population as an excuse whenever per capita income comes up?

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Occasionally, when conversations about per capita income arise,
people always spout irrelevant nonsense like
"it can't be helped because the population is so large"
or "but doesn't the large population compensate for it?"
To be blunt, I'm mainly targeting those who are obsessed with Japan.
I mean, if income levels were almost the same, it might be better to live in a country with a large population.
But if there is a massive difference, does it even matter that your country has a large population?
It's not like you are the King or the President of that country;
as an ordinary citizen, having a high per capita income is the absolute priority.
Of course, you have to look at various factors like the wealth gap, inflation, working hours, and social infrastructure,
but macroscopically, per capita income converges significantly with the standard of living for the common people in that country.
For example, in the case of Korea vs. Japan,
Korea is already a country with a sufficiently large population anyway,
and since Korea has lower inflation and a smaller wealth gap,
there is no denying that as of this year, Korea is the wealthier country.
And regarding Luxembourg vs. Japan,
this comparison is a perfect topic to bait those obsessed with population size,
but regardless of population, if you have a normal IQ, being born in Luxembourg is the obvious choice.
I'll say it again: you are just an ordinary citizen, not the state.
You are not the Emperor.