You may be interested in several previous AskHistorians discussions on related topics:

• Did the ancient Greeks consider Titans to be gods alongside the Olympians? How were the Titans viewed? Were there any significant groups dedicated to venerating the Titans, or other non-Olympian figures in the Greek pantheon? from 3 days ago
• Were the Titans the gods of a pre-Greek society that was supplanted?
• Did the ancient Greeks ever worship the Titans?
• How did the Ancient Greeks view the Titans?
• How did the Cronus / Zeus story come about?
• Who did the Romans worship before they conquered Greece?

It's generally hard to explain why something did not happen, as opposed to why certain gods were worshipped, but you should be able to find out Greek/Roman attitudes towards the Titans et al.