Ever played a relay race?
That's kinda how UPS/FedEx/USPS (basically non-freight) work.
You give them a package -- they pass it from driver to driver until it gets to where it's going. Those drivers operate under a certain class that is not the same as a semi.
For freight, your truck, it's going to be on a class of truck that has a special set of DoT regulations. Among these regulations are breaks. Not brakes like brakes like brake caliper -- but break like lunch break.
Some of these brakes are literally more than one day.
So, why does it take so long? Look up DoT regulations for driver breaks and you'll loose your mind.
Essentially -- you've got a guy driving around that has to exit the highway and find a place to park and take a break every X hours. So his 30 minute break instead of being 30 minutes is really an hour or two because that's just how things go, realistically. Then every X hours over Y days they have to stop and take a 34 hour break.
Now, you're a driver -- you're human, you don't want to take your 34 hour break just anywhere so you plan your trip so it sucks less while still providing that you have a good place to stop for what will most likely end up being 2-3 days.
There you have it. A one week haul by a vigilant driver turns into 2+ weeks largely due to regulation. Otherwise that driver would most likely bust chops to get things delivered and get back home to have a break they could enjoy more.
You also have to factor in there dealer time -- let's say they've got 10 cars going to 5 dealerships each of those 5 stops probably takes 2-3 hours to deal with unloading, paperwork, etc.. Ideally they'd all be going to one dealer and then you'd see much faster delivery times but with the drivers days all chopped up by stops and unwanted DoT breaks -- it gets stretched out.
Likewise, that results in pissed off drivers who go find loads to carry that are a straight shot so the rates go up. On and on, it's a mess. Almost all of which can be traced back to government action that itself can be traced back to corporate lobbying under the guise of safety with the reality of stifling independent and small operation competition to big corporations.