Why do people use 172.x.x.x instead of 192.x.x.x [closed]

There are multiple reasons to do so.

1. Your University is probably running this network since back in the days when there were no subnet masks and the private 192.168.x networks were Class C networks, limited to 255 machines. 172.x were Class B networks with up to 65535 addresses.
2. More important, if you want to allow VPN access to a network from people's home like many universities do, you need to avoid having the same network address that these people have at home. So, if you run a corporate or organizational network with remote access, you will choose something not in the 192.x range since that is what most home routers do.

There may be other reasons, but these are the two I know of.

There are three private IP address classes you can use in (private) networks. You choose the more convenient class for your network (depending on the size and thinking about scaling), so it is a standard but the answer of why the class C (192.168.0.0/16) is the most used is because the home/lab networks are not big and this class provides you with 254 /24 sized subnets available, which is more than enough.