They have steadily been increasing the amount of CGI in the films, a little at a time as they master it. They don't generally like to use a new technology whole-hog (ala Jurassic Park) until they are sure they fully understand how to use it effectively. It was also too expensive for them fore a lot of years. The average budget for a G-Film was only about $10 million.
Have a good morning, everyone! I'll check back this afternoon or evening sometime, have fun!