It depends on the infomercial, the product, the program, the timeslot, the hosts, their goal, the company, the company's history, the station, their goal, the station's history, etc. etc. etc.
There's probably none that "make money" for a sponsor on their own.
As part of a broader marketing campaign, they might help make money. If you see the same infomercial on a hundred tv channels, then it adds credence to the product/company. If you only hear it on a brokered rimshot daytimer, not so much.
If it's all that they do, like Carleton Sheets or that Morrison kid with the Internet Millions, then it probably makes money, but only for a short time, until the market is saturated. However long it takes for people to recognize what the real purpose of "sharing my secrets" is.
It all just depends. I don't know if they are "a great way" for stations to monetize their ad avails, since they tend to be about colon blowing and superlative health claims and get-rich-quick schemes, but they are apparently one growing way for stations to scrape up a little money.