By Oquendo from Freeport, NY (Patillas, Puerto Rico) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
If DC becomes a state than territories like Guam and Puerto Rico have further justification to become states. Many in these areas oppose this because the autonomy of the regions provides many benefits.
Only democrats in these areas support the measure and this is so their party can obtain more control in the US government, it also means more federal funding for these areas. This would only further push the national debt and reinforce Democrat power in Washington.