Why do you do this?

I started with crappy little rust prone Italian sports cars. Having survived that, I moved onto marginally crappy German cars. The cars got newer, arguably better, but a whole lot less fun to work on.

I lost a lot of my mojo for the hobby and slid into motorcycles. What fun! Simple. Inexpensive. Just like those cars I used to tinker with.

Sold the advancing tech of the Sacred Roundel and bought a 1960s American car. Simple. Inexpensive. Such fun to work on.

I'm nearing 60 and my desire to "drive fast and take chances" has diminished significantly. I've left racing, don't care about car shows and have no concern about impressing anyone. My joy comes from futzing about in the garage fixing old stuff and making it work properly again, then driving/riding around and enjoying the sounds and motion of my success. It's a satisfaction I don't get from my regular job. And at the end of the day, I have something in the garage that most people seem to think is cool.  That part is just a cherry on top.

A man's got to have a hobby.

As a kid, I used to play a lot of racing games (Gran Turismo, etc.) and grew around people who were car enthusiasts (Family, friends). After I got my license, I did enjoy cars and all but I found that I enjoyed the driving aspect of it more. I didn't really need to drive a special or quirky car in order to enjoy driving around although I have driven some interesting cars. A little under a decade after getting my license, I found out that all those video games I played in real life were accessible to me. I started doing track days, autocross and wheel to wheel racing and I love the thrill of driving a car fast and skillfully. It also was a good way to experience a lot of personal growth in multiple aspects and meet new people that were like-minded. Right now, I'm stuck between racing and doing other real life things but I still love it.

Keith Tanner said:

I've never cared about impressing other people or trying to drive something different just because it's different.

I like cars that do a good job at what they're trying to do. That might be providing lots of feedback and quick responses, or an effortless highway cruise, or getting somewhere most others can't. I wrench to make the cars keep working, to allow me to afford them, and to make them better at doing what I want them to do. And I have multiple cars because some of those things I ask them to do are at direct odds with each other.

That pretty much sums it up for me.    I've always had an interest in cars since I was little, from the Hot Wheels/Matchbox toys, to RC cars, until I was old enough to start with real cars.  Nowadays I can't have multiple cars due to the cost here, but peak for me was around 20 years ago, a Citroen BX TZD (intercooled turbo diesel) as a super comfy, quick enough (it stood in for the TR7 on one event and we took a class win!) daily driver that did 50mpg (UK), the TR7 V8 as the competition car, and a shared Range Rover Classic and S3 lightweight Landy for days out in the lanes.

I've always worked on my own cars, mostly out of necessity, but I've come to realise I do actually like it (sometimes).

I just can't cope with only having an appliance, the closest would be the recent/current Mazdas, but they're all reasonably fun to drive and have all been "tinkered with".

I love a good road and music up and no traffic. It's just relaxing. And an amazing stress relief. And rewarding after making adjustments or changes to the car. 

For me it's because anything can be art, when you put work and soul into it.

I was born this way.

When i was a kid in the 1970s, the Sears catalog had a car section. They sold wheels and tires and mufflers and such. I was a little kid, less than 5 years old, and my dad couldn't keep me out of those catalogs. I'd dream about chrome wagon wheels and Keep On Truckin floor mats. 

Then when I got a little older, the car magazines entered my life. 

Then everything cascaded from there.