anyone recommend a frame triangle bag (full triangle) that opens to the left non-driveside of the bike? for mtb frame

the Revelate Designs ones look great, but sounds like the main compartment opens to the driveside
what's with that btw? so far all the bags I've seen open to DS
if I mount dismount and walk the bike from NDS would it not make sense for frame bags to also face that way?

thanks