They are not. Tesla cars are level 2 autonomous, which is basically advanced cruise control. A feature found in many luxery cars before Tesla was even founded. With this level the driver needs to be aware of everything around the car and the car itself. Keep a hand on the steering wheel and be prepared to take over at a moments notice.

Tesla is currently facing lawsuits because they have branded one of their systems as Full Self Driving, implying level 5, but in reality only being level 2. There are also lawsuits involving the selling of an upgrade package with the car, which promised a higher level of autonomous control. Even though Tesla full and well knew that they weren't even remotely close to being able to do so. Since it was highly unlikely, borderline impossible, for the purchaser to actually obtain said upgrade, selling such a thing would be illegal. They also faked many demos and promotional material. A prominent example of this was a video of the car driving around a city, with Tesla claiming the car drove itself and the driver didn't do anything. Later footage leaked showing the car behaving erratically, veering into a cyclist, before the driver performing an emergency stop. Both occupants were shocked and nervously laughed off the incident. This was one of many incidents on that trip which didn't make it into the final video, but was leaked later.

Other brands are well ahead of what Tesla can do. But when we look at for example the Waymo cars or the stuff Toyota has been trying out, you can see the thing has sensors all over the place. Along with a roof mounted array of equipment. Our current level of technology requires this to be able to drive safely. Tesla cars don't have any of this, they even cut back on the number of high tech sensors in order to cut costs. Especially during the chip shortages caused by logistical pipeline failures due to covid. A lot of brands can actually produce self driving cars. The problem is costs, the equipment needed would double the price of the car, pricing itself out of the market. They could add it to fancy vehicles, but to be honest, once you can afford a Rolls Royce, the price of a human driver becomes a rounding error. But many brands offer and have offered level 2 for some time now. I personally have had experience with the excellent system Volvo has been using for years.

The only unique thing Tesla ever did was lie about what their products were capable off. And to the shock of the industry, they got away with it, with their market value exploding. It makes no real world sense to value Tesla above other big car manufacturers, even if their claims were true. It's a bubble about to go pop.