The early 90s was mostly a perfect storm for fuel economy.

You had the computing power available to make use of CAD and develop more aerodynamic designs with less significant overhead (i.e., doing it by hand).

EFI technology had matured and carburetors were broadly defunct, allowing more efficient operation in a broader range of environments.

The US had updated its archaic lighting regulations to allow for more aerodynamic headlight shapes.

A lot of the safety technology that adds weight to modern cars either hadn’t been developed yet or hadn’t trickled down to the average vehicle.

So you had a confluence of more efficient engines, more aerodynamic vehicles, and cars that were still small and relatively lightweight.

To be fair, if I don’t get off on a tangent I usually end up going around in circles.

Between needing to be able to service warranties on new cars and parts commonality across different models, it makes sense for a manufacturer to contract their suppliers to continue to produce parts outside what’s needed for initial production (to a point).

After all, if a warranty outlier or defect develops down the road, it’s a lot more expensive to reinstall old tooling and restart production than to just have extra parts on hand.

The aftermarket also plays some role, especially when you get into vehicles with longer service life applications (trucks, emergency vehicles, taxis, etc.)