The IS doesn't have an EV drivetrain, it has a hybrid drivetrain. No point in fitting a huge battery and a decent petrol engine together, the weight would be too much, and Lexus owners do not want a small petrol generator as a backup.
Teslas are starting to suffer long term reliability problems. Owners are complaining of battery packs and motors needing to be replaced, along with other issues. Toyota have a long established reliability reputation to protect, one reason why they haven't moved to Lithium Ion batteries.