The reason the Titans don't appear in many myths is because of the Ages of Man. To answer this question, you need a little backstory first. In the Golden Age, the primordial deities (first gods) ruled the world and Underworld. Gaia was the earth and Ouranos was the sky. They were mated and had many kids. Long story short, Gaia got her kids (specifically the Titan males [minus Oceanus]) to over threw him as king and Cronus claimed the thrown.
Fast forward Cronus was also bad (he ate his kids as soon as they were born) and his wife, Rhea, hid their sixth kid and gave him a rock to eat instead. When Zeus (the sixth kid) was all grown up, he served as Cronus's cup bearer. One day, with the help of Metis by some, Zeus put some mustard (or an emetic, by others) in his cup and had his dad puke up his siblings.
After a ten year war called the Titanomachy, Zeus and his five siblings defeat the titans. Most are sent to Tartarus (the pit) as punishment. But some, like those didn't partake in the war, didn't. The ones who remained neutral were left alone. The others that did were punished differently. Atlas's punishment for helping Cronus was to hold the sky up for eternity.
Then Zeus named himself king and thus started the Silver Age.
Prometheus was a beneficiary of mankind. Because of this, he was seen as less of a titan and more of a god, but still being called a titan. In other words, a titan is a god, but a god is not a titan. All titans are gods, but only titans are titans.
Gaia was loved as any other goddess. 'Oaths sworn in the name of Gaia, in ancient Greece, were considered the most binding of all. She was also worshiped under the epithet "Anesidora", which means "giver of gifts"'
After the Silver Age, Titans aren't really mentioned as most were in Tartarus. Those that aren't are often just called gods or Titan gods. Examples: Helios, Titan god of the sun, a guardian of oaths, and the god of sight. Selene, goddess of the moon, sister of Helios. Hecate, goddess of magic, crossroads, witchcraft...