Nobody said Pro amps couldn't do it too, but not everyone buys pro amps. There's a difference between "home concert" and CONCERT levels. I get the feeling we're not talking about live venue levels here. Pro amps are designed with more abuse in mind as well. My previous two Marantz integrateds, both had separate everything for each channel, except the power supply. I'll guess the Pro amps are more along those lines as well.
Another aspect of monos is that each power supply reacts only to the load of the one speaker; not sharing with the other(s). If the demand on the amp isn't to the point where that's a factor, as in the amp has sufficient headroom to handle the load, that isn't as much of an advantage. Effectively even with a two or more channel amp, the same would apply - if it is powerful enough for the load for the desired SPL then you don't have an issue.