Why are shunt resistors in BLDC motor drivers placed betweent MOSFETs and ground and not MOSFETs and the motor?
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. H-bridge output stage showing feedback for first channel.

As can be seen from the sketch, ground referencing the current monitor makes it very easy to monitor the signals. They will be low voltages and easy to amplify, manipulate or feed into an ADC.

The alternative of high-side current monitoring requires differential amplifiers, high-voltage protection and possibly opto-isolation. While it may be do-able, it's more complex.

Data sheet page 4 says, "Input
of
current
amplifier
1
(connecting
to
positive
input
of
amplifier).
Recommend
to
connect
to
ground side
of
the
sense
resistor
for
the
best
commom
mode
rejection."

I can't quite make out from the data sheet what the max voltage is for SN1, 2 and 3 but a lot of the analogs seem to be 7 V max.