It's a complete nonsensical myth they are bringing in money to Thailand.
There was nearly 3 million visitors from India this year, and they are still by person some of the lowest spenders in Thailand, yet makeup a large part of the visitors. A better way to look at it is spend per tourist.
Counting how much visitors from a certain country bring into the country is not an exact science, and not a perfect full proof equation. Furthermore, they do have some high end tourists who will spend money, movies shot in Thailand, but they also have some awfully budget visitors - to then average this up and claim Indians spend money is a bad way to look at it.
Secondly, you have to look at the impact they have on other visitors and local culture. They are sex pests, and whilst this is tolerated normally ... what they do is bordering on abuse. I have witnessed many of them, in packs hounding a Thai prostitute to give them a discount if she takes the whole group. The vulnerable lady will often agree. It's disgusting.
Many female friends refuse to go to Pattaya anymore as Indian men will often see them as prostitutes. It's barbaric. Their view on women is horrific. Furthermore, they've colonised other seedy nightlife areas in Bangkok, and other nightlife area which in turn has then meant a more higher spending clientele has moved away from entering those areas. Many clubs around Soi 13 in Bangkok, are aghast how they have bough the 'tone down' to that area.
The impact it has on high end tourists who will not want to go to resorts or destination where the makeup is of massive cheap indian tourists (along with Chinese tourists). No other country has a generous visa policy for Indians than what Srettha Thavisin in his stupid panic for more tourists has given the Indians. Why don't Indians let in Thais visa free?
So if they in turn then turn away high spending tourists, their net benefit further negates.
The economy of India per person is three times less than Thailand. Many will overstay and seek to work, all now possible thanks to the ridiculous open door visa policy for long stay.
Many other countries are now putting barriers back up to Indian visitors, eg Cambodia and Malaysia. But not Thailand. They will often say 'oh Indians bring so many millions to the economy', negating the fact the volume and negative impact they bring.
Pollution, litter, enviromental impact, over staying.
The problem will only get worst as more and more will come. You can only assume ex- leaders like Srettha have very little day to day mixing with these types of tourists so they don't care.