my question is this; carb vehicles last forever; why do ECU cars fail? as their designed to do exactly that
Carbs don't last forever, and they're always giving crap. The only people who think carbs are wonderful are people who never spent all day on Saturday fiddling under the bonnet trying to get their old banger running in time to fetch the girlfriend in time for the party that night. And then missed the party, lost the girlfriend and still couldn't get the bloody thing working properly, until about fifteen minutes before the road house closed at 1am and they came and rolled the pavements up for the night.
They're temperamental, need fairly regular maintenance to run properly, can be pretty good (either consumption or power but not both) and there are very few mechanics left who understand and can get a carb working well. But they are no match for a decent fuel injection system.
Your problems mostly come from the fact that the car you bought has been modded by some cowboy who hasn't a clue, and you're now paying the price for his mistakes. It's unfortunate and I feel for you, but it's not the typical experience.