The Taycan is roughly twice as expensive as the equivalent Model S Tesla and has greatly inferior range and, among people likely to buy electric cars, presumably less brand value. People haven't forgotten VW's emissions scandal. Let's not forget they haven't even shipped a single Taycan yet. BMW has sold a crappy, overpriced electric car/washing-machine-lookalike for years (i3) without it catching on.
Furthermore, there's no real competition on the horizon just yet for the Model 3. Tesla have a 3-6 year head start on making electric cars which will be difficult to overcome.