If someone is required by US law to file a tax return our ability to enforce that law isn't affected by their citizenship status. It may be affected by geography, but that's true for citizens and non-citizens alike.
Again, can you give me an example of a law that we can enforce against citizens but not illegal aliens?
I’m giving you an example. A US citizen overseas must file tax reports with the IRS. A Mexican who was in the US illegally has no requirement to file with the US IRS.
Why the difference? Answer: because the US citizen is ‘subject to the jurisdiction’ of the US government.
The illegal Mexican is not.
“Again, can you give me an example of a law that we can enforce against citizens but not illegal aliens?”
Draft laws.
How about “immigration laws”? Successful evasion of our immigration laws are what makes the person an illegal immigrant.