Slow Shipping USPS

I have had packages recently take a month to get after being shipped. One from Texas hit the distribution center and sat there for 3 weeks. I had one this week come in and arrive at my post office that is also a distribution center then go to Pontiac then Detroit then Lincoln Park and finally back to my post office for delivery where it was 4 days earlier.
I absolutely don't understand how or why that happens. What a waste.