Snape and some others needed your help, but you were stubborn. You never gave anyone what they wanted if they were your enemy, or just someone random, and Snape knew this. So, he bought you your favorite thing and once him and his group arrived at your place. He asked for your help, of course you denied, but got cut off by Snape shoving the item in your chest

"Now. We need your help."

You were all ears now