Why Do You Think Stevie Peaked Commercially with Bella Donna?

[skuncles]

Bella Donna was a perfect storm in terms of timing.

She was the darling of Fleetwood Mac
Her first single was with Tom Petty who at the the time was himself riding a wave
MTV hadn't yet changed the radio landscape or Top 40 radio
The album, like Rumours, is not a victim of the musical trends of its era

Everything Stevie did after BD would be affected by the influences of MTV, her status as really being a hold over from the 70's, and just the normal lifespan of an artist. Elton John once said every artist, no matter who they are, gets about five years where they are at their peak, after that they may still have hits, but nothing like those five years. For Stevie those five years are 1977-1981.
It's also interesting to note that Bella Donna didn't really earn #1 status. It got it as a favor, Pat Benatar actually sold more albums that week and Stevie should have been #2 but a deal was worked out to let Stevie get the #1 spot for one week. This story comes from the head of her record label, Danny Goldberg.