I am not sure if it is that, as we have seen some large assembly H-Go projects on Main Streets, such as this one:
developmentmap.calgary.ca
Perhaps a developer on this site can confirm, but I suspect it is more a case of the H-Go product being much less capital intensive. Sure you don't get as many units to sell/rent, but you don't have the cost of a parkade or elevators, or likely a lot of other expensive building code stuff I am not aware of. Plus, you can build them a lot quicker, so much shorter financing costs, etc...
It works for the developers, and maybe it isn't a bad thing in the end, but I feel if we are not achieving our planned for density on our nodes and corridors, it will make achieving our broader goals of curbing sprawl that much more challenging. On an individual project level it may not be a big deal, but imagine of even just 50% of the 37th STreet corridor built-out as H-GO, that would be a missed opportunity on likely several thousand units that could be on that corridor.