Illegal immigants do file and pay taxes, most with ITIN's - to the tune of ~$100B a year. https://itep.org/undocumented-immigrants-taxes-2024/
Most pay at a higher rate than USC's as they don't get the same tax breaks, and they pay in to programs they can't access i.e. Medicare, social security etc. So I don't think there's anything missing in the situation just because they've been paying taxes, most undocumented workers do.