I was a young Assistant Scoutmaster when the ISP and skill awards came to be. While things like camping, cooking, swimming and lifesaving were no longer required, the scouts in my troop, and I suspect many others, continued to earn them just because we did not change the way we operated our program. We were big on camping and hiking regardless of time of year, and if you were active in the troop those no longer required skills were developed and honed as a result.
I did like the fact that for a while First Aid MB was required for First Class.