Superliner is not just west of Chicago. We’ve been on them and see plenty of them here in the East.
Unless they scaled that back, too. I admit my last was 19 years ago.
They aren’t found on any trains in the NEC between Boston and DC due to low clearances. The Capitol Limited from DC to Chicago via Pittsburgh and Cleveland runs them but nothing north of that. The Auto Train uses them and the City of NOLA between Chigago and, well, NOLA as well.