Why is the same coffee taste better from a coffeeshop than homemade?  

I believe the biggest difference is going to be water temperature and time. I don't know the exact temperatures, but I understand that to get the best cup of coffee, your water should be within 5 - 10 degrees of a specific temperature, and the coffee grinds should only be in contact with the water for like 5 or 6 minutes.

The commercial coffee machines that places like Dunkin' Donuts use are probably much more consistent and reliable than a home coffee machine.

I'd suggest getting a coffee press, and heating up your own water. You can use a candy thermometer to be sure it's the right temperature before making your coffee. That's what I do (well not with a thermometer anymore) and I think it turns out greater than any drip coffee pot I've ever owned.

make sure your coffee grounds are finely grounded and packed as much as possible. it can also be perhaps your boiler is not hot enough. try adding a bit more coffee grounds for more flavor. ultimately, play around with the proportions. experiment.