He has to start somewhere.
His main appeal is in the urban areas currently.
I agree that he should go to Peshawar, Quetta, Karachi and various other urban areas as well, but Lahore is a good place to start.
Quetta, Karachi, interior Sindh etc. have a much stronger 'ethnic card based politics', which will be harder to break into without some sort of momentum, not to mention what I said previously, the ANP+PPP+MQM would rather see Karachi burn than allow IK a successful rally and eat into their support base, especially the MQM.
Now that the MQM has kissed and made up with the PPP again, the PPP might look the other way over MQM violence to prevent the PTI from becoming successful. I don't know if IK can win over some support from ANP leaders in Karachi, which might help.