A number of factors. Games were much smaller then and a competitive game could be done in 1-2 years by 2-4 people. The budgets were usually in the 5 digits. This made it much easier to do if you knew how. On the flip side, far fewer people had any programming expertise.

Now, it's possible to do something similar on the web, or with a cheap mobile game, but in console gaming (PS3, 360 etc) the games all run in the 8 digits (over $10,000,000!) and involve big teams, often over 100 people.