Why are wireless plans sold by data instead of by bandwidth, like wired plans? Don't sell me 20 GB/mo, rather sell me 1.5 Mbps min capacity with the ability to

Why are wireless plans sold by data instead of by bandwidth, like wired plans? Don't sell me 20 GB/mo, rather sell me 1.5 Mbps min capacity with the ability to burst if the network isn't congested. It's the bandwidth which is the constrained resource. Obviously there might sometimes be physical factors that prevent even the minimum.