why don't some people have a computer or laptop?

I have a PC. Not a fan of laptops

Perhaps they neither need nor want one.

They may find a portable 'phone adequate for their needs.

Or perhaps they cannot afford one - even more so if a software supplier like Microsoft moves to making all its products available only on subscription, so we would pay far more in total than if by up-front, one-off purchase.

Maybe they never felt the need, and they don't do work that explicitly requires a computer.

You can do so much with a smart phone these days.

Most likely can't afford one. Otherwise don't want one.