1. Model X sales aren't great, compared to SUV vs sedan sales for other manufactuers.
2. Other manufacturers have multiple mid-range sedan models. Honda has the Civic, the Insight, the Accord, the Clarity, and the Fit hatchback. Their sales are being split across five different low-mid-range models. Tesla has one. Toyota has the Yaris, the Corolla, the Prius, the Camry, the Avalon, and if you're some kind of lunatic, who for some insane reason wants a hydrogen fuel cell car, the Mirai. Again, for other auto manufacturers, sales in the same price/specs/form factor are split across five different models.
3. There's no reason to believe that five different Tesla sedan models are going to lead to anywhere close to 5x the demand. I mean, maybe if 4 of them are ICEs...