Being a self published studio isn't just about having a lot of money (though that's often a prerequisite, at least for AAA games). There's also experience with

Being a self published studio isn't just about having a lot of money (though that's often a prerequisite, at least for AAA games). There's also experience with marketing, relationships with console manufacturers, market research, negotiating platform pricing. Publishers' knowledge of these things make it useful for a studio to still team up with a publisher even if the studio is swimming in cash.