The updated python libraries needed for CHIRP no longer work on Win7 and will not be updated for Win7 as Win7 is no longer a supported operating system by Microsoft. CHIRP development has moved on to the updated libraries, and therefore has dropped support for Win7. Some people are upset that NEXT won't run on an older operating system, although nothing is stopping them from using the last supported CHIRP version indefinitely on Win7, they just won't receive support or newer features.

Time moves on and so does computer support. I can't complain CHIRP doesn't run on XP either..