Why should I buy a car in Cyberpunk 2077?

I get constant messages from fixers urging me to buy a car.

Yet I wonder: Why should and would I invest money in them? They are not cheap, and apparently, I can't customize them.

And through progressing the story within my Nomad playthrough, I unlocked two bikes and two cars very early and they all seem pretty decent.
The Archer Hella EC-D I360 was shortly damaged but repaired early in the Delamain quest line. After Jackie's funeral I got his bike from his mother. As a Nomad, my old car got activated allowing me to buy it cheap for 100 Eurodollars from Lana. And during Panam's sidequest I got Scorpion's bike.

Is this merely a money sink to allow me to buy a fancy car for bragging rights?

Or are there some quests or races attached once I buy some of them?

Solution 1:

There is no benefit other than having an additional choice to ride around in Night City.

There is a car racing quest with Claire from Afterlife, but you can always choose to pick her ride instead, and in one of the races you are even forced to.

Solution 2:

Many of the cars you can buy are better (faster, more durable, better handling) than the ones you get for free.

Every vehicle in Night City is a unique mix in its characteristics, and many are substantially more or less pleasant to drive than others. As for not being able to customize your ride... you’re looking at this the wrong way. Buying a preem new set of wheels is how you customize your ride. No, there’s no paint shop. But with literally dozens of rides to buy or find, you’re sure to find one that suits your style.