Yes, key changes went away in US pop music at some point a few decades ago.
But the idea that this has to do either with hip-hop or with digital music production is frankly ludicrous, and the author presents zero causal evidence here except that all three things happened very roughly around the same time. And the proposed explanations make zero sense.
The real answer is simply that the shifting the key up in a dramatic energy-raising fashion just went out of style, like a thousand other things in music. As the author themself notes, they're "heavy-handed" and "trite". I could add corny, old-fashioned, and overly earnest to that list.
Everything in music gets overdone and then fades away to make room for the next new thing. There's no more reason needed for this than people just got tired of the old thing -- which they always will.
Claiming it's because of hip-hop or digital music is just strange.