CNNs were a pretty simple idea even at the time. People were using convolutions for years already in classical image processing. It's a small step to put those computations into weights. Especially if you leave out the FFT step which neural nets don't even use.

Low hanging fruit successfully plucked, I guess.

I sometimes find myself thinking this too then challenge myself to find a low hanging fruit in an area I’m somewhat familiar with and draw a blank (usually).

Low hanging fruit is somewhat the opposite of sour grapes - I don’t want these grapes because they were probably sour versus so what if he got those sweet grapes - they were hanging low!

Maybe connecting “low hanging fruit” to “sour grapes” is “low hanging fruit” to some but it took a serious mental leap for me.