Sikhs do not have their own country, why do they need their own calendar?

Sikhs do not have a country of their own. Does it mean that we, the Sikhs, should not have a calendar of our own? The Bahai faith is the newest faith, being about 200 years old. Its followers gave up on the Hijri calendar and had their own calendar based on tropical year length and permanent correspondence with the Common Era calendar. All major religions of the world have their own calendar. Why should not ours?

The following quotation from ‘Mapping Time’ says it all:

“Today each of the major religions has its own calendar which is used to programme its religious ceremonies, and it is almost as true to say that each calendar has its religion. The Christians, the Moslems, the Jews, the Buddhists, the Jains, the Hindus, the Zoroastrians, and, more recently, the adherents of Bahai, all have their calendars.”

-Richards, E.G., Mapping Time, p.6