Also different people use the same car at different times, etc.
(And as others have alluded to, a house is a much more stable environment than a car. It takes a LONG time to make most houses significantly warmer or cooler, a car's internal temperature can change drastically in minutes.)
My partner enjoys ambient temperatures about 3°C warmer than I do
Depending on which of us is currently in the sun, or which of us is alone, you need to vary it quite a lot in summer
In winter, you want the AC for defogging but not on otherwise, which is even more fiddly if you don't just leave it on permanently and use like 10% more fuel
And that's assuming climate control works. It doesn't in any car that I've ever been in. The car doesn't want to sound like an airplane at lift-off once the temperature goes 2° above the set point, while I may just have come from a long walk and am super warm and want this blast of AC air. And then after 5 minutes it gets chilly and maybe I want it to cool the car instead of blowing at me directly, or maybe I just turn the loudness down. There are so many permutations... I suspect we may be built differently if you are happy with a single set point!
I'll set the temperature differently if it's cold vs hot out, and in some weather have to tell it to unfog the windshield.
Because sometimes it is hot.
I want more cold air blown on me at a higher velocity until I cool off, and then to be a steady state. Even if I had remotely started my car with air conditioning, which although my vehicle has the capability I never do, the seats and steer while and other things I touch will be hotter than the ambient air temperature and make me feel hotter until the car has been moving a while.
Because people are ... different?
I'll start with your home example. I grew up in a hot environment. Everyone had window ACs and fans (way more efficient than central AC for many types of homes - but that's for a subthread).
With a separate AC and fan, you have two variables you can tweak to get your comfort: Speed of air, and temperature. Believe it or not, some people are not comfortable in a cool room if they're not getting air (and likewise, many/most people are comfortable in a warmer room as long as they get air).
Then you move into a house with no fans and just a central AC and ... it sucks. So you buy pointless table top fans to compensate.
Same with cars. It's not just about the temperature. It's about air. With modern EVs, as I pointed out here[1], it's (almost) impossible to get warm air blowing on your face in cold weather.
Finally, there's the "obvious" reason that applies both in homes and in cars. The temperature you need to feel comfortable keeps fluctuating, and depends on outside conditions. In cold weather, I need to set the car at 70-71F to feel nice. In hot weather, I'll throw up if I drive at those temperatures - I need 60-65F. Same with my house: In winter, I set it to 68-70F to feel comfortable. In summer, I just get cold at those temperatures.
Having a constant temperature in the car doesn't help me if I make a turn and suddenly the sun is coming on my half of the car. Being able to quickly dial down the temperature and have air on my face will cool me in under 10s. Merely dialing down the temperature will take several minutes. Similarly, 10 minutes later when the sun goes behind the clouds, I'm suddenly cold because I don't have the sun compensating for the AC. Merely turning the fan away doesn't help. I need to raise the temperature and keep the air on me to normalize (again - the difference between seconds vs minutes).
If you've never gotten used to that, I can see why you'll settle for something vastly inferior.
A simple example: With my car, I can remotely start the AC. When I've parked the car in the sun, I can start the AC (max cool) 10 minutes before I get in, and it's still a bit warm (but at least not hot). If instead I get into a really hot car with no AC pre-conditioning, it will take at most 1 minute for me to feel cool if I have the AC blowing right at me.