some have nefarious(crime/tax evasion/etc) reasons and others just don't want to get exposed i assume.
i knew a chick for a long while who worked at peiwei with a stolen SS# and peiwei actually encouraged it and hired a few of her friends too. she's still in the USA last i checked and still has never filed to become a citizen. it's been well over a decade now and closer to 2 decades since i met her. i hold no ill will against her or any other illegal alien but i just smh when they are exposed, deported, and cry about a situation they should've resolved many many yrs prior. there's no tears shed for those breaking the law and doing so for yrs and yrs because they figured they'd never be caught.