Only this can create problems of its own. Some dealers will refuse to work with you if you are paying with actual money instead of a loan. My parents went through this. They sold some farmland and decided to buy a new car with the profits. A few dealers simply said no. The car they wound up with mostly depended on where would actually sell them the car.
You could also be missing out on incentives from the manufacturer for not using their financing. It's definitely a good idea to have money or financing already lined up, but some manufacturers will give thousands of dollars in incentives to use their financing.
There are probably cases where the current incentives are rolled up in the financing, e.g. 0% interest. But there are also often other fees and, frankly, the available (effectively) risk-free investment options these days have such low rates of return as to be almost indistinguishable from 0%.
They're not giving you deals on the financing because they like you.
If I were buying a car my very strong default is to just pay cash and be done with it.
Those incentives come with costs. In their case, it was better to know they didn't have to worry about making a loan payment every month for years when their overall financial future was a little iffy at the time - prudent when the main income earner's health was failing. It wound up being the correct decision, as my father died a couple years later.
My last vehicle I had cash to pay for it. Manufacturer offered a $2k incentive to finance through their own financing arm. I asked, and there was no early payoff penalty. So I financed the car, and sent a check a week later, paying it off completely well before the first payment was due.
They bank on screwing people over with financing. I didn't tell them how I'd be paying until we were signing paperwork already. He wasn't happy to hear a I will be writing a check. Then I refused to sign the arbitration agreement and he really got mad, but oh well I got the car anyway. However it wasn't a pleasant experience overall.
Some simply aren't willing to do the paperwork one must do with transfers over 10k. More importantly, they make more money off of the loans than they do with cash. This is true even if they must repo the car later on - they can often sue you for at least part of the total cost, minus the amount they sell the car for (that last bit might vary by state, though).
Also, when people say they're paying "cash" for a car they don't necessarily mean they're walking in with a stack of hundred-dollar bills. "Cash" often means cashier's check, etc. - the idea is that you're not borrowing money to buy the car.
Only this can create problems of its own. Some dealers will refuse to work with you if you are paying with actual money instead of a loan. My parents went through this. They sold some farmland and decided to buy a new car with the profits. A few dealers simply said no. The car they wound up with mostly depended on where would actually sell them the car.