In theory at least it’s because you pay for a specific bandwidth for home internet (the size of the pipe) but a specific amount of data for cellular (how much stuff you can get through a fixed sized pipe).

Home internet is a little unique in that way, almost all other utilities are consumption based with no real tiers in terms of how it’s delivered (you pay for the volume of water or gas you use, electricity is the same, just different units).

Networking equipment gets more expensive based on the bandwidth it supports, but it doesn’t much care how many bits you push through it. So ISPs charge based on their capacity to deliver those bits, and provide tiers at different price points. Cellular though is much more bandwidth constrained due to the technologies (and it used to be much more so before LTE and 5G), so it didn’t makes sense to charge you for slow or slower tiers. Instead the limiting factor is the capacity of a tower so by limiting data to small amounts it naturally discourages use. That model carried forward even now that the technologies support broadband speeds in some cases. As such and ISP could provide the biggest pipe (highest speed) to all homes and just charge based on consumption (they used to in the days of dial up, and satellite before starlink always has). Many ISPs instead are now double dipping though and charging for both.