Tesla's charging equipment itself is just flat out more reliable than competitors. AFAIK they re-use modules from their vehicles ganged up so benefit highly from using an automotive grade battle-tested component. It also means there are plenty of spares available for replacement.
They also have a lot more "boots on the ground" so to speak so when a station needs service they have someone within a few hours drive at most who is capable of fixing it and likely has the parts on hand. They aren't relying on a bunch of random franchise operators to maintain equipment, nor contractors who are touching an EV charger for the first time and may need to order replacement parts that take months to arrive.
I have seen some people discount the vehicle-to-charger billing system but that is also a reliability factor. Not having to maintain a payment reader is one less thing that might break. It also means the charger can operate even if it loses network connection... it simply queues up the billing records and reports them once connection is re-established. Auth via an app or NFC terminal usually requires internet access which adds yet more points of failure.