Tesla rightly judged the EV market as being (at the time) a luxury car market.
With or without credit most buying Teslas would still have bought, however those buying Leafs, Volts and iMievS very much had the credit as a consideration.
To grow the regular consumer car market towards EVs would require intelligent regulation like right to charge, subsidies that target the middle lower income alongside proper and predictable tax policies.
So Going forward EVs being popular as luxury cars may not hold and Tesla will either adapt or fail