Because they are unnecessary. In many cases they cause more injury then assistance. My wife is small and sits close to the steering wheel, she'd probably be injured pretty good if it went off. Stuff like that. It probably wouldn't affect me much as I am taller....people have even suffocated from them before.

The MB safety cell and seatbelts provides excellent protection.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)