Yeah, I used to think so too, Bluedart and Delhivery.
Was actually shocked to see India Post after long time, but then it's SBI. So, I am not surprised if they are using govt postal service.
@RishiKiDev See, for areas with limited connectivity, India Post seems fine because India post delivers to all the pin codes. But when other (and better) options are available, SBI still chose to use India Post.