Why were the noble gases so difficult to detect and isolate. (More details on background)?

Question

The noble gases were among the last naturally occuring elements to be discovered, even though, some of them, particularly argon and neon, occur in moderate abundance on Earth.

Why were the noble gases so difficult to detect and isolate.

Answer 1

They are colorless, odorless, and tasteless. They don't react with anything under normal conditions. People simply didn't know they existed, and then could not find a way to isolate them from air since they didn't react like other gases.