Because there is no more space :)
The VL Discovery has only 128k flash, and there is some space reserved for saving code, so the board can run code standalone.
You can compare the board files, for example PICO vs VL Discovery. That Discovery board only includes
neopixel, and has
SAVE_ON_FLASH - removing bunch of features. While the PICO has USB, networking, graphics, encryption etc libraries built-in.