Mainly because the Indians could acquire a starter before the deadline. The key date is Derek Lowe's next start, which on Tuesday, just hours after the trade deadline. If they acquire a starter before then, I could see that starter taking Lowe's place, and Corey Kluber taking Tomlin's place until Roberto Hernandez is ready. If no starter is acquired, then the Indians would likely have to choose between Lowe and Tomlin (and this point, it's probably Lowe) to stay in the rotation until Hernandez is available.
The Twins are getting SS Eduardo Escobar and Pedro Hernandez. LHP Escobar has been a reserve infielder for the White Sox this year, so he'd be some competition at the major-league level for Brian Dozier and/or Alexi Casilla. He may actually play third initially with Trevor Plouffe now on the DL. Hernandez also saw some time with Chicago this year, though it was very limited. He's spent most of his season in AA Birmingham, where he's posted good ERA numbers (2.75) but not very good peripherals. Neither of these two players look like they have big upsides; if they work out, they'd be bench/bullpen players.
In the meantime, the Twins will be sending Brian Duensing to the mound for today's game, as Liriano was slated to start.