If they made something that was just the sensor and logic board that they already manufacture, and sold it for exactly the same US$149 retail price _or more_, there are people in this thread who would buy it.
That’s not enough volume for Apple. This is a company comfortable sitting on $100bn in cash.
If they sold 1 million of those, it’s not worth it for them. Even 10 million units likely isn’t something they’re interested in, and I doubt they’d see anything close to that.
100% - they quit the much more lucrative WiFi business. The funny thing is the post, the likely the most interested party, who already spent $150+effort on a keyboard with TouchID admitted they are willing to spend $50. Literally the most excited customer who pays $150 is expecting a lower price than the keyboard. That simply shows the existence of such product is counterproductive to Apple's total revenue.