That's the only one I know of at my bank that's mobile only. (And for how frequently I deposit checks, going to an ATM wouldn't be a big deal.) I realize other banks may have more de-featured web sites.
Because sometimes you want to check banking services on the go. Or you get a notification on your email and want to open the app to check. Or it's much quicker to log in with fingerprint. Or so you can quickly zelle someone on the go. Or because why do you want to go and pull out our computer and turn it on and log in and waste all that time when you have mobile computer in your pocket that's always on and always connected and not in your backpack in the corner somewhere. I know a lot of people who only have a work laptop and use their phone for everything else.
Why not a computer?