4 day cricket for a Test playing nation is like training and sparring sessions for a pro boxer. It doesn't exist to make money. It exists to sharpen up the national team so that they can go out and win games of cricket, and winning lots at international level is what makes people want to tune in and watch you, and that's what makes you money. Without a strong domestic cricket system, your will struggle to produce new talent, and your existing talent won't have a place to go to outside of international games that will keep them sharp or challenge them to improve.
I'm going to play out the boxer/international cricket team analogy now, not because it needs explaining, but because I like it:
Very few people care to watch the pro boxer train and spar. Boxers can't monetise the training and sparring. It costs them money to do it - pay a gym, a coach, potentially pay for training partners, pay for equipment and medical care. And that's on top of regular daily costs. Training is basically a sinkhole for money for them with no real return.
Boxers only earn their money by fighting real fights. That's what the fans pay to watch. Fighting as much as possible ensures the boxer earns as much as possible.
The catch, however, is that people don't pay money to watch boxers who suck. It's the best boxers* who earn the most money. To have a large fanbase of people willing to see you fight, you must be worth watching. You must be a good boxer.
How do you become a good boxer? You spend a lot of time training.
You put the money and the time in to train and spar at the gym, with the coaches, the training partners, the equipment, so that when you do go out and fight, you put on a performance that enhances your reputation. This then increases your fanbase, and thus how much you can earn from future fights. The training and sparring doesn't directly earn you the money. You don't do it because it turns a profit. You do it so to strengthen your skills so that when you go and fight, you perform well, and that performance earns you the money.
Investing in your domestic structure is the same as a boxer investing in their training. You invest for good pitches, good coaches, and you try and ensure the best non-national talent also stays in the system and keeps playing. Because this is the breeding and training ground for your national talent. And if this is strong, then your national team talent is strong. And when that is strong, you will win lots of matches. And when you win lots of matches, you get more fans, more sponsors, your TV rights are worth more, and overall you make more money.
You don't use domestic cricket to turn a profit.
*yes I know the best boxers don't always make the most money don't start nitpicking me on this
