Re: Why?
not sure everyone is staying on topic here.
its a valid question to ask, why remove the banner if it isnt in your view Islamically valid to mourn for longer than 3 days. but then shouldnt you also ask why you’re exchanging greetings specifically on a day that the Prophet never ascribed any significance to… since you’re basing your greetings/non-greetings on Islamic tradition.
Posters here object to celebrating basant for example, on the grounds that the Prophet designated certain days for celebrations, and we should stick to them, and not be influenced by other cultures. It is a pagan tradition to celebrate their respective new years too, I dont see them raising the same objection here 
, dare i say hypocricy?