beyond the obvious 'do it to show that i can' and similar reasons, one less obvious reason may be that often people want to mod these games and its easier than

beyond the obvious 'do it to show that i can' and similar reasons, one less obvious reason may be that often people want to mod these games and its easier than either making a reproduction or using hacks. Having the actual code the game runs (even if decompiled) allows you to both learn how things were done, as well as modify them and improve them. Many people starting out in games development often want to make games like RPGs to emulate a favorite game they play, but want to experiment with their own rules/mechanics