There are various reasons for it: a sense of alienation and exile in a strange land, and attempts to preserve one's own pride and dignity in preserving one's culture and traditions.
Culture plays a significant role in one's life. Shared beliefs, values, behavior and a way of living give a sense of belonging and a sense of community to a person. To a person living in a foreign country where exists a different mainstream culture, his own culture becomes even more important. It is to overcome the sense of strangeness and alienation in the different land, even he himself does not consciously recognize it.
What is however interesting is: when these same people return to their native land, usually they try to follow the mannerisms of the people of that foreign country they were living in. Whereas they were feeling a sense of inferiority ( if one might say it) in that foreign country, a sense of superiority tend to mark their behavior after their return to their native land. They become, in the process, displaced and discontented human beings.
I often visit San Jose in California, USA where my both children are settled and have seen that there are many Hindu Temples like Shri Siddhi Vinayaka Cultural Center, Sunnyvale Hindu Temple, Fremont Hindu Temple, Balaji Temple etc. The people here observe all festivals - not only Holi and Diwali like festivals but religious festivals like Karwa Chauth, Navratri, Ganesh Chaturthi etc. also.
Often festivals are celebrated at community level on next weekend instead of on the day of festival itself. Holi celebration in the campus of the Stanford University is most famous in this area.
As far as cow dung cakes are concerned, the same are available online in India also on portals like Amazon and eBay etc. Some buyers ask for gift wrapping also of cow dung cakes.
Let us encourage each other in sharing knowledge.
The migrant people have a sense of detachment and possible guilt/yearning that they could not visit a temple, they could not do a pooja, they cannot have a physical place of faith wherein they can seek spiritual solace.
So, in short what is at plenty here in India,is short overseas. Hence to have 'a link' a bond' with Indian traditions the migrants have huge temples, halls built. In Birmingham, England, the Balaji temple would be crowded with Indians, naming and head tonsuring ceremonies would be linked for the families to see in India, residential programmes for students in vedic life would be conducted. In Eastham area of London, there are so many temples, that many Hindus feel at home.
In Neasden the Swaminarayan temple is a famous place for Indians to congregate, any visit to the Welmbey Stadium who automatically mean a visit to the temple in the morning or early evenings.
Today I read in what's up that many of us crying and longing for homely food only when we happened to eat hotel food.