Why don’t Sikhs wear two Kirpans to represent Miri & Piri like the 6th Guru?
As per the hukam of Guru Gobind Singh, the tenth Guru, and the Panj Pyaare, Sikhs must wear a kirpan. We can wear more than one, but the minimum is one. Guru Hargobind Sahib, the sixth Guru, wore two kirpans in a deeply symbolic gesture to show the importance of spiritual (piri) as well as temporal power (miri), but he did not give a hukam to his Sikhs to do the same, nor is there any record which suggests other Sikhs did so.
Many Sikhs do wear two kirpans (one smaller and one larger) but that is a personal choice.