It's no single thing because people's decisions are affected by the sum total of their life's balance sheet.
The labor market is something that emerges from the equilibrium of several opposing forces. We as a society decide which causal factors are 'reasonable' and which are 'unfair'.
As a simple example, you could argue that 'the wages for married individuals with kids are depressed due to the massive labor pool of single people in their 20s who can be employed for far less as long as you offer them free food and some cutesy perks like happy hours and pool tables'. Ceteris paribus, and as a pure fact of economics, this is true. Of course if you have a bigger supply of labor and hold other things constant, wages will depress, but as a matter of practical policy, we don't consider it 'unfair' that there exist single people who are competing for jobs that married people are also competing for.
But many people do consider it unfair that there exist Indians who are competing for jobs that Americans are also competing for.
This is a matter of policy and your personal sense of what is fair and what is not, not economics.
Should you have to compete for your wage in comparison to individuals from a foreign country with a much lower cost of living? For the most part you can't change your cost of living. (Yes, you can move else where but the delta between how you you keep/earn is pretty much relative around the country)
Single people tend to be younger and less experienced. They tend to be represented in entry level positions, and get paid as such.
>Should you have to compete for your wage in comparison to individuals from a foreign country with a much lower cost of living?
That appears to be the reality we've been living in for a couple/few decades. Airplanes, container ships, and the internet have made the world a much smaller place.
The labor market is something that emerges from the equilibrium of several opposing forces. We as a society decide which causal factors are 'reasonable' and which are 'unfair'.
As a simple example, you could argue that 'the wages for married individuals with kids are depressed due to the massive labor pool of single people in their 20s who can be employed for far less as long as you offer them free food and some cutesy perks like happy hours and pool tables'. Ceteris paribus, and as a pure fact of economics, this is true. Of course if you have a bigger supply of labor and hold other things constant, wages will depress, but as a matter of practical policy, we don't consider it 'unfair' that there exist single people who are competing for jobs that married people are also competing for.
But many people do consider it unfair that there exist Indians who are competing for jobs that Americans are also competing for.
This is a matter of policy and your personal sense of what is fair and what is not, not economics.