Well it's pretty simple actually. Let's say they both earn 50k per year right now for working 10-15 hours a week. If they put twice the amount of time to actually release stuff on schedule, they might earn something like 80k each per year (or maybe even more as they would own the market completely and could do more commissions). It's all about ambition and the lifestyle you want for yourself.
With this extra money, you can get a nice house, enjoy high-end restaurants, give a great life for your actual or future family, retire early, all while only working 20-30 hours a week while also being your own boss. That's some great conditions right there that would be totally worth it, even if you have to put in some effort. Note that these numbers are very rough estimates, don't put too much weight into them*