It all comes down to expense though. You could throw the whole kitchen sink into the computer but then how much would it cost to manufacture and how much would you need to sell the thing for?

Costs need to be cut somewhere and micro computers had to additionally ship an interpreter ROM (typically some dialect of BASIC), more expansions ports (for printers, serial modems, memory expansions, additional storage devices, etc) a physical keyboard, and so on.

Plus lets also not forget that while many micros were sold as games machines - they were originally built as hybrid devices for doing work, finances, etc as well as recreation.

There was a lot of "serious business only" attitude in many of the computers those days.

On a console you typically have a circular buffer and the screen is a movable window on it, so you only have to paint one row every time.

https://www.atarimagazines.com/compute/issue67/338_1_Atari_F...

On the C64 that’s 8k which is a lot if 16k is all you get (the video chip only has enough address lines to address 16k).

I was envious as hell on my MSX, which had no pixel shifting at all.

Vertical scrolling changes the timing of the bad lines and horizontal scrolling the timing of the bitmap data fetched and this causes the image to come out at a different position.

There are a lot of creative tricks you can do with this though, especially with vertical scrolling.