BLDC Motor Driver: Justifying better design approach
one of the most important points is power handling

using individual MOSFETS will give you a very wide range for how much power it can give you 

for example
if your BLDC require 30 or even 50 amps to reach its max power(torque and speed) I think it will be hard to find off-the-shelf integrated circuit that can support this amount of power, usually at this case there is no escape from using individual transistors to handle this power

also heat dissipation is a big problem you must handle in your design

in case of using ind. Trans. it would be much easier to distribute the heat over multiple packages instead of one package which would be in the other case the IC

one disadvantage is the size of the final design

sometimes you need the minimal amount of components in your design, but if you will use multiple MOSFET approach you will definitely need a controller also (microcontroller as an example)