If I was a Thai woman, I'd be looking for a farang to take care of me too. Because once they get to their forties, fifties and sixties, the future is pretty bleak.
Some Thai women are abandoned by their husbands or partners because they are no longer beautiful, or they have a child/children the Thai male does not want to support.
Presumably there are Thai men who remain in a marriage, even if they play around, which I understand is quite common. Mia nois and giks. Having said that, I am astounded by the number of quite attractive Thai women I meet that are single, and not by their choice.
It's a contract of mutual support. I can expect to be looked after when I am messing my diapers, in return for the money I provide.
A case in point is my regular Thai massage lady. 60 yo, hard worker. When she was 30 yo, her husband told her she was no longer beautiful, and split. Her daughter hasn't spoken to her for years.
She's actually better off than many rural Thais, owns her own house, car, and scooter. However, if she stops working, she will only be getting the government handout of 500 or 600 baht/month, which is a sick joke.
Standard questions I get from just about every middle-aged Thai woman are "Where are you from?" Second question invariably is " Do you have a Thai GF?" Quite sad, really.