DC prohibits cooperation with US Immigration and Customs Enforcement, which is vital to fighting human trafficking, drug trafficking, gang activity, and other threats to DC public safety.
Here’s an article from 2018 that describes some of the horrible crimes that have been committed by people ICE is trying to remove.
The Council recently passed a bill that continues to deny district participation with federal law enforcement when they are trying to alleviate our prison system of violent criminals.
Additionally, the DC jail is populated by a lot of Ward 8 residents in a poorly-resourced jail, according to this news article.
Finally, DC may receive more federal assistance if it cooperated with the federal authorities. It’s politically easier to accomplish than achieving statehood.