Two main reasons
First, it's the only company that cultivated a dedicated audience of handheld gamers
Sony tried but their studios are simply better doing cinematic stuff that plays better on TVs. Third parties who wanted to cater portable gaming all went to mobile which essentially left Sony alone
Second reason is their appeal to older audiences. Yes older, not kids. Kids play anything you show them. What Nintendo caters is their parents who think Nintendo is a safe choice. Humans are product of habit, and no company exploit habits better than Nintendo







