Winning a race is not the same as being a factor in the season. He had one win, which was St. Pete. Outside of that, he only had 4 other top fives. He DNF'd four times as well and was out of the championship hunt as early as Pocono. That is not being a factor.
Going to your second statement. Money is an issue regardless of series. Montoya however, could easily pull in big sponsorship. Just two years ago he won the Indy 500 and was tied for the series championship. Had you read the article, it said that he was offered an drive at Indy, which he specifically said "is the only one that matters" and if Penske get a DPi program set up in IMSA, they'd have him there since he is interested in it. Montoya is not going to be overlooked by someone like Draccone, Fillipi, or any other pay driver. He can bring his own money to the table and has success. The problem is that a lot of the field have merit by talent and have the ability to bring sponsorship because of that talent. The only teams that are looking for money primarily are Ed Carpenter Racing, who are favoring Hildebrand and Pigot because both have performed well within the team and have great sponsorship because of that, KV Racing because Bourdais left, and if Carlin merge with them, Ed Jones or Max Chilton will have a ride there, Jones the Indy Lights champion, Chilton coming off a season where he really impressed with how he improved. AJ Foyt have ABC Supply for both of their cars. They aren't even looking for sponsorship. CGR, if looking for sponsorship, have a lot of people to choose from like Sage Karam, Santiago Urrutia, and Zach Veach. Is money an issue in motorsports? Yes, it has been for decades. But Montoya's situation is not a byproduct with that.