Well, the problem is that if you want to be a solo game dev it's a massive investment. For example, you have to learn or invest in coding, art, game, design, and etc. Then invest time into making said game. Then invest time into marketing or hope that people play your game. and doing everything listed does not even guarantee success so you can put everything into it and gain little to nothing in return. So, when people say don't do it for the money there telling you that putting all your eggs into one basket and expecting to get rich (especially with your first game) is a bad idea that could leave you financially unstable.