Here's the (pretty pedestrian and likely not different from a b/w tv) diagram of the horizontal driver for a vt220: https://imgur.com/a/xvq1ukV
The shown MC1391P is, in fact, called a "horizontal TV processor" by Motorola.
I'm sure there's other stuff that made them expensive (CPU, memory, video logic, etc).
Edit: Lol at imgur for marking my screenshot as "erotic" and NSFW.
https://imgur.com/a/yJH9QYu
(Which Imgur also finds erotic and NSFW. Odd)
Here's the (pretty pedestrian and likely not different from a b/w tv) diagram of the horizontal driver for a vt220: https://imgur.com/a/xvq1ukV
The shown MC1391P is, in fact, called a "horizontal TV processor" by Motorola.
I'm sure there's other stuff that made them expensive (CPU, memory, video logic, etc).
Edit: Lol at imgur for marking my screenshot as "erotic" and NSFW.