Why would anyone prefer public transit over a self driving comfortable personal car?

Because public transit, done well, is the fastest way to move around. It gets you everywhere, even to places personal vehicles can't reach. It's a lot cheaper. It generates hubs of activity that keep cities lively and relevant. It doesn't get stuck in traffic. It doesn't need to be parked.

The benefits of good public transport are so mind blowing that it's difficult to explain unless you have lived on a city that has it.

In addition to the other good reasons also raised, PT has much more optimal land-use than private cars. Train stations or metro stations take up relatively little land and can be integrated with business and services or have nice public plazas and small parks. Compared with multi-lane highways, parking lots, giant intersections that are hostile to pedestrians and active transport.

Because it’s available to everyone, including kids and elderly, and does not need high upfront payments.

I can just move to Madrid and move anywhere in the city for around 1-2€ per trip without upfront investment of 20.000€ for a car, plus insurance, maintenance, fuel and taxes.

Trains don't get stuck in traffic, and some of them have restrooms and space to walk around in. They're also better for the people outside of the vehicle.

Why would anyone prefer a self driving comfortable personal car over teleportation?

Why would anyone prefer a car that YOU have to drive over an autonomous all terrain comfortable personal horse?

A horse knows how to navigate any kinds of terrain, while a car requires constant microsecond attention, extremely stressful, if you lose focus, might end up dead, worse kill a lot of other people! Horses don't need roads to be built, or the elaborate supply chains of fossil fuels, and trillions of dollars per year in subsidies.

Because of the lesser impact on land usage, fuel usage, noise, ...?

Why would anyone prefer airline transit over a comfortable private jet?