The more generic your prompt, the more generic the response. It's a regression to the "mean" of the training data aka GIGO for AI.

It's like when you ask your average person off the street to draw a house - it'll almost always be square with a triangle roof, one door, and two windows.

In the pelican/bike example, it's probably a bit of a self-perpetuating snowball too. If the earliest examples were bike left-to-right, flat ground, etc. then they are also being scraped up in future LLMs.