That graph might be more because it's not as exciting. Google searches are probably dominated by hobbyists and casually interested people. If they're not trying to achieve a specific goal, then they might prefer to work out the basics and make it themselves instead of just taking part of someone else's work and reusing it. If you were going to do that for fun, why not go the whole hog and reuse an entire pretrained network?

Personally, I'm a hobbyist and I don't want to know about these shortcuts until I start to need them - which is a stage I might never reach. People who've progressed far enough to need them are probably far fewer than those who are just curious what these words mean.

Another possibility is the words "transfer learning" might be more generally meaningful outside the ML field than the other search terms on the graph, so most of the searches for it are really schoolteachers or something else.