Internal pull-up resistors not really effective

Thot

Hello,

I use a lot of Single Board Computers and the point is that when I use internal pull-up/down resistors, I always have spurious floating input with spurious push button. (true on Raspberry Pi and ODROID)
Now, on SBC, I always use external level resitors.

On the UpBoard, on the pinout wiki page, we can see :

The SoC GPIO pins include configurable internal pull-up resistors, but these are not really effective when the level translators are configured in input mode. If pull-up or pull-down resistors are needed for stabilizing floating input signals on a header pin, the user would need to include these in the external circuit connected to the UP board.

I is the first time I see this "not effective pull-up resistor" and I am curious to understand why is it not effective.