Почему только bei vielen, если это якобы общая практика для всего андроида?

Это общая практика, но начиная с версии ОС Android 6.0 пользователь должен высказать своё информированное согласие с тем, что есть теоретическая возможность определить местонахождение устройства по Bluetooth. Раньше она тоже была, но согласие не требовалось). Поэтому «bei vielen» имеются в виду пользователи андроид, начиная с 6 версии.

Почему для активации Wi-Fi оно не требуется не знаю, там то же самое.
Тут подробнее:

applications using Bluetooth have direct access to the device MAC address for the purpose of pairing. I will assume this for this answer.

If you can read MAC addresses of WiFi or Bluetooth transmitters, you can locate a device. This is how WiFi/Bluetooth location works; you listen for MAC addresses of transmitters and look these up in a giant global database.

Therefore, any application using Bluetooth and a data connection is theoretically capable of locating your device. I am not sure this is practically possible; Bluetooth does not have the same range and semi-permanent access point infrastructure as WiFi.

By requiring location services to access Bluetooth, you ensure that the user understands their location information may leak when they use Bluetooth. In versions of Android prior to Marshmallow, the user could use Bluetooth without location services enabled, but location information could leak. In these older versions, you could also run WiFi scans to find MAC addresses without location services enabled, which again meant that your location information could leak. The requirement to allow location services to use Bluetooth is about ensuring that someone who disables location keeps their location private.