Well they wouldn’t stay in business for long if their competitors were receiving govt incentives (ie tax breaks), were genuinely greener and had cheaper ticket prices.
The carriers don't build their own planes. The tech is sold to them by the manufacturers, e.g Boeing & Airbus. The carriers will transition to "cleaner" planes when they're given to them. The people will pay the costs.
The carriers would pass the costs onto the people flying. Penalising them.