MX Blue not clicking

[Zeppelin]

I have a old keyboard, with cherry blue, that are not clicking. They are working, but not clicking. Is it because of spring, or because of the bottom part (copper parts inside housing)?

[daedalus]

I've found before that dust or hair can get inside the switch and prevent the clicker from working. However, the age of the switches can't be ruled out as a cause - tactile/clicky Cherry switches don't age that well, and they can feel less and less tactile as they get older.