Chips have a higher value on a BOM, and as such have more financial incentives to be reverse-engineered and counterfeited. This is a bit more interesting since it's a sensor that has several operating parameters that "sort-of" send expected data back, but depending on the operational characteristics could need to be recalled entirely.

Especially if they are to be used for something like monitoring for excessive heat in some kit that could catch fire.

If this was used in a BMS with a lithium battery, a counterfeit sensor's behavior could result in the total loss of a device. Let's say the device's PCB is designed such that the sensor is connected to a rail that requires parasitic power, and you were unexpectedly shipped the D1 variant that outputs garbage data back to the onboard firmwre instead the proper temperature. Your company would have to recall every device in that manufacturing run at great expense, if it weren't caught early enough by QA.

This particular sensor isn't used in mass produced devices AFAIK. NTC thermistors are cheaper and easier to design for using cheap analog components. Reading DS18B20 is quite an exercise when it comes to $0.05 microcontrollers used in e.g. household appliances.

That's true in an analog design, I recently took apart a generic computer power supply that failed and noticed it used NTC thermistors. In a hobbyist kit I purchased that came with with various cheap sensors, the temperature one has a Dallas 18B20 on a board to be interfaced with an Arduino. It's probable that some people would just duplicate exactly what they used on a quick-and-dirty design to be deployed on a small scale.