Why don't SFs around the world use bullpups? Even those countries which use bullpups as the primary weapon for their infantry don't use them for their SF. Like Australians or the British.
Bullpups with side ejection ports make weak hand shooting very difficult, the brass hits your face. If they make it forward eject or bottom eject, malfunction clearing becomes a chore as you cant see inside the chamber. Bullpups generally have shittier triggers. Handguards dont provide enough railspace for mounting accessories.
Alot of these issues can be solved, but it still ends up being awkward to shoot because of its ergonomics, you cant even adjust the length of pull.
Its easier to just go with an AR variant then to dedicate time and money into a new rifle that solves these issues.
The only thing bullpups achieve is being shorter in length, but the special operations community have found ways to deal with the length of their conventional weapons at such a degree that it isnt an issue anymore.