That is true, but let's compare some similar products.
The Tesla UMC is a good 32A device, which only costs $275.
The equivalent thing from Clipper Creek is $484.
store.clippercreek.com
The Tesla wall connector 48A capable device is $500.
The equivalent thing from Clipper Creek is $899.
store.clippercreek.com
So with like-for-like kinds of products, I don't see why people buying Tesla cars would overall be driving people to buy more expensive charging equipment from outside sources.