"Unbelievable" and "unforgivable" eh? It's a greedy attitude. Instead of viewing GTA5 as a success that's brought a lot of people happiness, you view it as a money cow designed to extract every last bit of profit – and time, since this bug caused 70% longer loading times.
Perhaps it's both. But you, sitting here behind a keyboard with (correct me if I'm wrong) no gamedev experience, have no idea what it's like on a triple-A gamedev team with various priorities. The fact that the game works at all is a minor miracle, given the sheer complexity of the entire codebase.
The fact that someone was able to optimize the obfuscated executable is a wonderful thing. But they weren't a part of the team that shipped GTA 5. If they were, they certainly wouldn't have been able to spend their time on this.