There's more complicated software involved in DC charging due to the much higher power levels, plus more complicated monitoring of the system. AC charging is much more straight forward and simple.
There are some nice conversion kits for things like classic cars where it makes sense to have fast charging. But then we're talking 50-60k in cost and a lot of labor. For that kind of money, you can get several decent second hand EVs or even a new one. Spending that kind of money is only interesting because it's a classic car. E.g. a lot of old porsches apparently drive a lot nicer and better after an EV conversion. Also not having them break down with weird mechanical issues all the time makes driving them more fun. Also, more torque, power, etc.
But you wouldn't do that with some generic consumer car where the whole point of the conversion is avoiding the expense of buying a proper EV. You can get some nice used EVs for under 10K now. Pretty decent ones even.