What can the reason be to choose this specific op-amp as a Comparator/Schmitt trigger?
Sounds like you have a sensor such as a variable reluctance type that has an output voltage that varies with speed. Such sensors inevitably have a lower limit of operation- at some point you'll have signal level that is too low with respect to noise and offset voltage of the circuit, so even if you wanted to make a circuit that would trigger at 0.0001Hz it might not be practical (or perhaps even physically possible, given inherent Johnson-Nyquist noise and such like). 

So, it's a trade-off that the designer of the circuit made- more hysteresis means that the circuit is more immune to noise near the trigger points, but it will have a higher minimum RPM. It's certainly possible to make a circuit that has almost no offset and almost no hysteresis- down into the single-digit microvolts- but that might not be the best solution from a system design point of view.