Why should the police attempt to assault and capture something like a house from potentially armed individuals? This fails basic tactics. You don't attack the garrison, you wait until they're on patrol and ambush them. Outside the home it's much easier to positively ID suspects to ensure these are the people you want. They have an equal understanding of the area around them, unlike their own house you've never been in. The ability to carry arms in a car is more limited than a home. Surrounding a suspect in a car is much easier than a guy holed up in the back bedroom with good angles. And frankly an overwhelming show of force can trigger people to simply surrender as opposed to being trapped in your home and deciding to fight it out.
At the end of the day we're talking about violent, potentially fatal operations all revolving around someone selling weed, coke, pills, etc. It's simply not worth getting cops, suspects, and most importantly innocent people killed over. If someone OD's because the operation takes more time, that's at least a person that made a decision to ingest drugs as opposed to an innocent neighbor or bystander killed for simply being in the wrong place.