Ratan Tata is an employee of the TATA group of companies where as Mukesh Ambani is the chairman of Reliance industries
Yes,it is true.
Now coming to your question
TATA’s donate 66% of their profit right away. About 66% of equity of Tata Sons is held by philanthropic trusts endowed by members of Tata family where as Mukesh Ambani donated Rs603 crores in the past year. His wife Nita Ambani is also involved in a number of philanthropic activities.
Mukesh Ambani is a businessmen looking to maximize his wealth where as Ratan Tata is an Industrialist, he believes in giving back to the people.
The net worth of Ratan Tata is not even $1 billion on papers.
Mr.Tata donates from his earnings that's why he is not the richest person in terms of wealth, but he is the richest person in terms of values,love towards his nation and it's people.
Moreover Tata's main focus is to build nation not profit.
Ratan Tata invests in small businesses with less profit like salt,mechanical work and the list is very long. You must have heard about the Tata's Nano, now you can guess why he is not the richest person.
“We are industrialists and they are businessmen”-Ratan Tata