were they just cheap enough for everyone to afford them?

Sort of.

Around 1975, there was a guy named a guy who worked at Hewlett-Packard.  His buddy got him some contract work for a little project called Breakout, which wound up being sold by these guys. 

Incidentally, all the components some company might need to build a computer were available to companies in the late 70s, but business practices at places like IBM and HP were geared entirely towards mainframes and minicomputers (suitable for huge companies with thousands of employees, or even medium-sized businesses with 500 or so people), or the industrial/corporate segment of the electronics market.  A "personal" computer back then was as preposterous an idea as a "personal" jet aircraft might be today.  Sure, everyone says they might want a Lear Jet, but not when it costs at least a million bucks and you still can't land and park it it anywhere other than an airport.  Anyone advocating a small, low-power device for home use, was be looked at as strangely as someone today might be for suggesting that GM or Ford should get into the personal jetpack market.

That led to things like the Homebrew Computer Club.  During their off-hours, engineers of all persuasions would get together informally and talk about what they were doing.  If nobody's going to sell you a computer, then by Glub, at least you could build one yourself and tell your friends what you'd done.  Maybe you could learn something from what they'd built, and maybe they could build something cool using what you'd built.

Back to that first guy and his buddy.  In addition to building blue boxes in their garage, they decided to try their hand at building a computer, and his friend convinced him to try selling the computers.  By 1978, there were so many geeks just itching to have a computer of their own that it was no longer possible to build them all by hand.

Back in the 70s, you had to build your computer from scratch -- finding individual chips, soldering or wiring them together onto your own circuit boards by hand -- weeks or months of labor before you could even turn the thing on, let alone program it to do anything.  Woz changed all that.  For the small fee of $666.66, you could start programming the instant you opened the box.  The rest, as they say, was history.

The closest parallel I can imagine in recent years was social networking.  Everyone's been able to have a custom web page for themselves since the mid-90s, but it was only when social networking sites made it easy for the non-technical user to maintain such a thing, that the idea took off.  As recently as 2000, it was rare to find anyone who had a web page of their own, but today, it's hard to find someone who doesn't have at least a myspace or facebook page. 

why were movies popular in the late 1800- early 1900's?
why were cars popular in the 1910s?
why were planes popular in the 1930s?

its all about accessibility. . .


In the 70s computer servers took up a large amount of space.... in the 80s they figured out how to put them in to desktops. Once they became smaller they became popular.

I love watching old movies from the 80s and earlier, and you see those giant computers that were 5 times the size of a refrigerator

The first computer I had was a Commodore Vic-20 from 1983.  It was handy, and could do alot of things that (at the time) would have taken longer to figure out or draw (math, charts, graphs, even learning, etc)

I remember watching an I Love the 80s episode on VH1 a few years ago where they had a tv commercial from 1981 showing the earliest laptop computer - it looked like it was about the size of a briefcase.

I remember watching an I Love the 80s episode on VH1 a few years ago where they had a tv commercial from 1981 showing the earliest laptop computer - it looked like it was about the size of a briefcase.


and those were just the compact size ones ;D