[Scoundreller]

My thought was to use the regen braking electricity for (more) resistive heating when it has nowhere else to go. It's an extra thing that only gets some use (depending on climate), but not a very expensive extra thing and takes some load off your pad/rotor brakes.

[ggreer]

The battery is warmed by the heat pump (or if you have an older model, the resistive heating coils). That component can only take so much power. A more powerful heat pump would cost more, take up more space, and weigh more. My guess is that Tesla designed their heat pump based on these tradeoffs.