- Incumbent auto giants entrance diminishing Tesla's margins.
- Incumbent expertise and brand that diminishes Tesla's appeal.
- First mover disadvantage: rest of auto industry sees large initial ROI by piggybacking off Tesla
GM can't be the only guys racing to bring Tesla experience to it's existing brand followers. Luxury makers like BMW, Benz will woo the lion share of the market Tesla originally pioneered. First movers rarely do well here unless they've cemented their brand position in the luxury space such as Ferrari, Lamborghini etc.
tl;dr: When the status quo catches up to Tesla, it will put downward pressure. Tesla's winning strategy should be to limit quantity and artificially inflate unit price. It is not equipped to take on dozen automotive brands in the long run.
Please correct me where I'm wrong.