several reasons, they fit the rack perfectly they are use for load monitoring and load capacity calculations, and generally support much higher loads then cheap strips,. prolly the biggest reason is the plug type, dc equipment generally uses c13-c14 plugs, and 208 power, you don't generally see that configuration in cheap strips. and at 400 and 900 dollars, they are a drop in the bucket compared to what the equipment costs.
i throw out brand new never configured equipment worth more then what my entire family will make in a lifetime, roughly once a month. fiber cables are NEVER reused, when removed they are cut instead of uncabled, even when a new machine is going to be installed the next day. i see millions wasted yearly, pdu's are not even a consideration in total cost for most customers.