Finding the right RTU to collect alarms from all your remote sites is hard enough - but then you've got to worry about how you're going to bring the alarms back to your network alarm monitoring master.
The problem is, you don't have a luxury of choice for alarm data transport. Who can afford to install new network facilities for telemetry data? So you have to use whatever transport is available at your sites.
And if your network is complex or changing, you can be working with different transports at different sites. You may prefer to use LAN transport, but you still have sties where only a dedicated circuit or overhead channel is available. You might even have very distant sites where the only available transport is plain old dial-up modem.
And the problem gets worse if your network is changing. You may need to install alarm monitoring right now, but you don't want to get a remote for serial transport when you know that the entire network will switch to IP transport in less than five years.
What are you supposed to do? Buy a different kind of RTU for every different kind of data transport you use? And then buy new ones when your data transport changes?