Depends of your goal. Making a 2D games it's very easy in terms to have tools to make it. Making a 3D games it's very hard because the community need to make and improve tools to make it.
Making your own tools (engines) or using some available from the community. You need to do a lot of research to know how the PlayStation 2 works and what tools are available today to help you in the game development process. You can start here: github.com/playstation2-development/ps2dev-world
How hard is it exactly to make a ps2 game?
Depends of your goal. Making a 2D games it's very easy in terms to have tools to make it. Making a 3D games it's very hard because the community need to make and improve tools to make it.
@ps2dev how did exaxtly developers managed to make games? Trough what?
Making your own tools (engines) or using some available from the community. You need to do a lot of research to know how the PlayStation 2 works and what tools are available today to help you in the game development process. You can start here:
github.com/playstation2-development/ps2dev-world