Why is shaving the beard considered forbidden, even though letting it grow is mentioned as part of the "fitra" along with matters not considered obligatory, such as using the miswak and plucking armpit hair, whereas the command to differ from Jews and Christians in dyeing is mentioned?

The problem concerning the exemption of the beard and its being among the sunan al-fitra (practices of natural disposition), which are mustahabbat (recommended acts), and that this indicates its non-obligation, is based on the "inference by conjunction" (dalalat al-iqtiran), which is not considered an evidence by the majority of scholars. This is because conjunction in wording does not necessitate conjunction in ruling. Furthermore, external evidence confirms the obligation of letting it grow.