Heat is one factor, being in a hot car could have affected it somewhat but on its own that wouldnt be enough to completely degrade all cannabanoids. If they were all degraded then all the THC would have turned to cbd and CBN which would have made you very sleepy. Ground flower looses freshness very quickly since there’s more surface area to react with oxygen/the air. You also probably just got sold some garbage bud like a REALLY low grade shake or even maybe already extracted leftovers like D3 suggested. Car temps generally don’t exceed 110f unless you’re car camping in death valley. The lowest cannabanoids and terps will start to vaporize is around 200-300f.

Always buy bud flowers intact and roll your own joints. If you don’t want to learn how to make a joint from papers and filters I recommend cones which are already preassembled and come with packing stick. Or just get a cheap bong or pipe.

Keeping the bud intact until your ready to grind and smoke will preserve its freshness and flavor.

With Good bud flowers you can visually inspect them they should be covered in crystals and small colorful hairs. Dispensaries can make this hard since all bud is prepackaged in non clear containers but most flower worth is smoke will at the very least have a moderate amount of crystals and hairs.

Sorry your experience was shitty and money was wasted, prerolls aren’t worth the $ IMO.

If you decide to keep smokibg and want cheap bud in bulk to mix in with the good stuff you can buy Delta 8 flower from online hemp flower sellers like industrialhempfarms which let’s you buy big 1 pound bags for 400-700$ depending on flower. It won’t be one hit wonder flower since thc9 has to be below .3% and the thc8 is about 5% through industrialhempfarms but my god it will last you months and months and will get you a little high.