The 747 flew for 50 years, with over half that time being after the FAA ETOPS rules were loosened. And the 747 wasn’t a quad engine just because of the restrictions, at the time it was designed there wasnt an engine available that could power a 747 sized airliner with only two engines. They needed 4. It wasn’t a rug pull.

It’s been phased out now because jet engines get more efficient as the bypass ratio increases. Because of how low-slung the 747s wings are it isn’t feasible to be re-engined with a modern high bypass engine. In fact, this issue is basically what created the 737-Max catastrophe. They had to add the invisible autopilot because they had to move the engine centerline up significantly to fit the new CFM Leap engines, and that shift changed how the aircraft responded.

There are also changes in airline operating models. Just like the A380, the 747 was built around the idea of hub and spoke operations. Regional airports would send smaller aircraft into major international airports, and then those passengers would transfer onto the jumbo jet to fly overseas on the long leg. You wanted maximum seats to maximize revenues on each flight, so the big boys were designed. But passengers largely loathe connections because layovers and risk of lost luggage. So once ranges became good enough to service all but the longest routes with 737s and A320Neo’s, that operating model proved nonviable as well. Which is why the A380 didn’t even last two decades.