I have a 2002 Toyota Tacoma, which was a mid-sized pick-up back when "mid-sized" actually meant something. I love it. Here's why:
1. I'm tall and it fits me much better. I have plenty of headroom, and the seat is high enough from the floor to support the backs of my legs. In many sedans, my heels get sore on long drives because they're taking much of the weight of my legs.
2. I like the better visibility. In particular, I have fantastic visibility out the back of the vehicle. Any time I drive other cars, I feel like I have blinders on and can't see behind myself well.
3. It has real steel bumpers. I once caught the edge of the truck on a fence and yanked the bumper out a few inches. To fix it, I just gently drove into a tree and pushed it back into place. Good as new. In most sedans with plastic covered crumple zone panels, that would be a thousand dollar panel replacement. A few weeks ago, I watched a poor parallel parker repeatedly bounce off my truck as she wormed her way into a spot. Not a ding on it.
4. It's a tank. The reliability of pick-ups is generally great because manufacturers have to cater to work truck consumers who care about reliability over all other considerations. If it's good enough for that landscaping company who puts 50k miles on it a year while hauling a trailing, it's going to be good enough for you. My Tacoma will likely outlive me.
5. It was cheap. Sedans are often designed to cater to an audience that wants superficial luxury and then charges people for it. I don't care about heater leather seats and touch screens. I just want something comfortable and solid. My truck was $18k new and I've gotten 18 years out of it so far. The amortized cost of ownership is incredibly good, even when you factor in the lower fuel economy.
6. It stores stuff. 90% of the time, the bed is empty. But that other 10% of the time is really convenient. I've moved apartments using it. Numerous camping trips. I lived in the bed for two days for the last eclipse. Dozens of trips to Ikea and the hardware store. When I was in a band, I put amps and instruments back there. I bought a couch on a whim the middle of a road trip. Sure, you can rent a truck for days you need the storage. But in practice, that can add so much overhead that you just do fewer things. If I want to hang some new closet doors or do some gardening, I can just go.
7. I like the way trucks look. Maybe it's a side effect of a childhood in Texas, but I like the design of older trucks. They feel simpler more "iconic" to me. They have an elegant form over function aestehtic. Most sedans all look the same to me. The parts that are functional -- the aerodynamics -- make them both and the other parts feel like pointless decoration. (That being said, newer truck designs turn me off because they're now all huge jacked-up monuments to masculine insecurity. The new Tacomas make me want to cry.)
Really, trucks are great, simple, cheap, utilitarian vehicles. People always complain that "the beds are empty 90% of the time", but 90% of the seats are empty in any given sedan, so what's the difference? A vehicle always has more capabilities than you need at any point in time. My truck doesn't have as many passenger capabilities, but it has a hell of a lot more hauling stuff ones.