That is because it is a convoluted federal bucket of crap
Actually, it's because there is no line at present that anyone would be required to go to the back of. People just say that to sound like their amnesty - let 'em all stay in the US - proposals have some actual penalty included.
The only going to the back of the line that would mean anything would be if illegals went home and applied to return legally - at the back of the line for legal immigrants in their native country.