Most of an airplanes stopping power is generated via the wheel brakes which are very efficient at converting the airplanes "go" energy into heat via friction using the brakes and tires. Also, generally thrust reverse capabilities are not used for calculating stopping performance. I say generally because some manufacturers have managed to certify some variants using them, the practice of which I'm not a fan but that's neither here nor there.
At any rate without the airplanes primary means of slowing and only spoilers to help create a resultant downforce to slow the airplane it's a simple matter of logic and physics that it'll take longer to stop since its not as efficient at stopping.
In short:
"blah blah blah, whatever, no brakes which is how the airplane stops."
