Why christians and musIims shouldn't and can't be celebrating Pongal?

Short answer: Pongal is strictly a Hindu festival. In other states, it is known as Makara Sankranti, Lohri, etc among Hindu communities in other states.

Long answer: read the thread

1/n

Pongal is generally a multi-day festival. Contrary to popular dumeelian understanding, Pongal is neither a special Tamil festival nor the real Tamil New Year as Mr Arulchelvan tried to justify back some time ago.
2/n

The day before the main Pongal day is known as BHOGI. BHOGI itself is a Sanskrit word derived from 'bhoga', which means enjoyment. The one who enjoys is called Bhogi. The Lord remains an enjoyer while we, jivas are the enjoyed.

3/n

This is exactly what Andal showed by leading us as an example. She observed the Dhanurmasa vrata and reunited with Lord Ranganatha on the last day of Margazhi, the day of Bhogi.
4/n

On Bhogi, a popular activity is lighting a bonfire early in the morning. The bonfire offers warmth in the cool and chilly morning weather. Fire also burns away anything that we put in. On Bhogi, the fire is light to signify burning our sorrows, materialistic desires,
5/n