There is more than one manufacturer of these little leds and they can be designed with different parameters. I’m guessing Sofirn, or whoever assembled the switch assembly, used a really low output green led. This is why they used such a small 1k ohm resistor.

I’ve got some lighted tail switches from Banggood or Gearbest that are blue and only use 330 ohm resistors and they are not even that bright. I think this is another example of a weak LED.