Probably because the actual event was on federal land so D.C. couldn't veto it and as long as it was going on we had to spend the money we did because it was happening or we'd have been worse off. The mayor is asking for reimbursement which needless to say will require some political pressure or it won't happen.Trump's hijacking of the 4th of July celebration cost the DC government $1.7 million. It came out of a special fund that is meant to protect the city from terrorist threats and provide security at rallies and events like state funerals and that is now more or less depleted. The article also mentions that the Trump inauguration never repaid the city the $7.3 million it spent. (Shocker. Trump hasn't paid a bill).
Why did the city not refuse to host the event/pay anything other than what they would normally pay (which, according to the article, would have been six times less) especially since they're still waiting for the money from the inauguration? If you don't pay, you can't expect service.