Mazda would take off in the US if you could buy them without going through a shitty dealership.

Most likely because higher-end EV swaps use Tesla rear drive units, which are fairly plentiful.

We’re starting to see commercial-off-the-shelf subframes for putting Tesla motors in classic trucks.

For example:

https://www.aemelectronics.com/products/ev_conversions/conversion_brackets/parts/HEV002-001