Just because Tamils don't help each other, it doesn't mean that telugus or hindi folks help each other. You are not just deeply involved with Telugus or hindis or gujartis. There is a special name for this, but I forgot: doctors see the incompetence of medical journalists, whereas physicists find these medical journalists extremely competent. In other words, familiarity in one domain makes them good judges of that domain; as a consequence, they commit a fallacy: they misjudge the competence of people in other domains one is not competent in.
Here are two examples from Telugu folks. One guy came to USA in 1997 on H1-b, and he even sponsored his wife's sister and the latter's husband for green cards. His wife's sister family moved to the states. They even had joint businesses. By 2006, this guy regretted his decision of sponsoring his wife's sister. My friend, another telugu speaker, was working at his check cashing places in Jersey city, NJ, while being on H1-B (this from 2006). Even though my friend took care of two check cashing businesses in Newark, NJ and Jersey cit, NJ, that boss did not want to help my friend. Now this boss owns five check cashing businesses, 50% of a trash collecting company (which he purchased from Italians). One lesson: never underestimate human emotions such as jealousy.
The second example from 2021. Another friend, a telugu speaker, was working as a contractor at a famous shoe company in Portland. One of his colleagues, a telugu woman, whose husband also works at the same company, gave him hard time by sabotaging him. How did she sabotage? When his manager gave him tasks, the manager asked him to take help from this girl. Whenever she share some thing, she hided the crucial detail, and this friend was on the wrong track. Later, this girl started complaining about my friend to the desi manager. Another Indian FTE came to rescue my friend, not because my friend is Indian, but he wanted to assess my friend objectively, and went through the code he wrote, and then helped him change some APIs. Later, this colleague warned about this girl to my friend: "she is badmouthing you in our FTE meetings, be careful with that snake". This is pure, plain jealousy from fellow native language speaker. Many don't want to see their fellow men from India to succeed at work.
Third example: Some Babu is both Tamil and telugu speaker. He claims he is tamil to Tamils, but as telugu to telugu people, because he comes from that part of TN, that is 20 kms away from Andhra border. This Babu told my friend many times: "how did you come to America, and you don't have good personal skills". My friend is more than average at technical stuff, but he lacks the skills of chamchagiri.
The list goes on: just ask gujarati guys about their experience with fellow gujjus, after making friends with them.
Marwaris and Sindhis do help each other (I am not talking about their helping each other in the states). In Andhra, many marwaris come from Rajastan to start samosa, chai stalls, clothing stores, kirana tores, etc. These people recruit 15 years old marwaris from RJ, and make them work for them for five years or so. After that, big boss helps these works to start their own business.
You know what non-marwaris and non-Sindhis do when they are given an opportunity to work for Marwaris in some gold shop or other place? First complaint: why should I work hard? If I work hard, my boss makes more money. Marwari workers work as if they are the boss of the store: they try to learn every thing to succeed as a business owner, as their goal is start a next business and the bosses are ready to help them. The attitude of Marwaris and Sindhis are differnt from non-marwaris/non-sindhis wrt business. Just like Phoenicians (ancient tradesmen, you can see modern phonecians in the successful Lebanese people in Mexico and Africa), Marwaris/sindhis learn "kuladharma" from their grandparents, they don't like to take shortcuts. That's why in many parts of Andhra, Marwaris have taken over, as vysyas/baniyas left the business because their kids are in USA or in Hyd/Bangalore working as software engineers.
In Vijayawada, during the covid time, one Telugu worker working for marwari jewelry store, ran away with 1Kg gold, as the owner got covid, and gave keys to this telugu worker to run the store.