I don't know what it is that makes it thus, I presume it is intentional as it's hard to achieve such universal shittiness. Usually there's a good dev somewhere and one product accidentally will have great software... but nope, not with Garmin.
I still cling to my Edge 705 because if I use it the way I use it (display track on the map, never use routing) I never have any problems unless I'm an idiot.
Garmin Connect is such a piece of shit of software.