Why do SIDs include an MEA? Let's say we're flying the JORJO2 SID (1,2) out of KPWK (RBS transition). We are told "climb via the SID". Page 2 of the SID says "maintain 3000" but the MEA on page 1 is 4000.

Is there ever a time we are supposed to climb to the MEA?  Or are we to maintain the top altitude in the SID (3000) until specifically cleared higher?  I'm just not sure what the purpose of displaying the MEA is on this chart, lost comms maybe?
Yes it's for lost comm.  If you look at the MOCA you still have the required obstacle clearance.  MOCA only gives you reception within 22 NM of the NAVAID, while MEA gives reception along the route.  If this was not an RNAV procedure I'd expect your level off altitude would probably be the MEA (just my assumption!).

In this case you would maintain 3,000' until cleared higher.  If you were to lose comm you'd fly the higher of filed, assigned, MEA, or expected altitudes.