When PAL Singh Purewal developed the Sikh Calendar , All the dates related to Sikhi were fixed and everyone agreed on all the dates except three
a. Hola Mohalla.
b.Bandi Chor,
c.Guru Nanak Birthday
Taksali ,SGPC and Sant Samaj was of the opinion that if Hola Mohla dates would be fixed than the event will get separated from Holi and eventually loss its significance . So it was decided when Holi dates is announced by Hindus in their Jantari the next day would be Hola Mohallah ,same is for Bandi Chor after Diwali.
Holi is a Hindu Festival just like Christmas is Christian festival .Whether as a Sikh u like to join or not is a personnal choice. But the dependance on Hindu Calendar logically our Leaders are making Sikhs celebrate Holi and Diwali .
Diwali is the biggest festival celebrated in India and maximum donations to Gurudwaras is during these times. Why would committee disturb the Financial Balance Sheet .