> I suspect it was the penetration of the Apple II into education and business that helped make it possible

I don't know how much it moved the needle but it was astonishing how much schools and home users - parents whose kids used the machines at school - were willing to pay for an Apple II well after it was a technically obsolete machine. It definitely helped them to some extent.

(don't get me wrong, I love those machines in my bones, but they were pretty overpriced after a while)

here's a guess: text was sharp on an Apple II with a decent monitor. font shapes were good. no matter how good graphics were on the C64 & Ataris, in comparison, text was always blocky & amateur looking. Tandy did better on this front, but it wasn't enough for them. pretty sure this is the same reason why the Amiga & the ST didn't make more inroads — people looked at them alongside the Mac & technical considerations were quickly forgotten. it's funny to me that this hasn't changed all that much — Windows font rendering looks awful to me, & I'll always pick a Mac or Linux box to use instead if there's a choice, just so I don't have to put up with the fonts. this wasn't always the case — the old system character sets used under DOS were pleasant to use.