Are all the 170s DCI? Maybe the ones that aren't will move over to DCI to replace ASA 700s winding down, and 175s will backfill.
Or Gojets is going TU and some of these will replace their 700s. Or Mesa is losing their United flying in those 700s and replacing them with E175s. Seems common theme here is Delta and United want to convert 700s into Ejets