A car tire is designed to operate within a couple degrees of vertical, whereas a moto tire needs to be able to operate at angles as great as 60 degrees from vertical. Because of that, traction is engineered into the profile over a much greater area of the cross section of the tire.
Car tires are engineered to provide traction over a large flat contact patch, moto tires are designed to provide traction over a much smaller contact patch that varies widely in position around the cross section. They are also required to handle larger side loads relative to the size of the contact patch. Because of those requirements, the rubber compounds used are softer and necessarily wear faster.
The problem with a car tire is that as the bike is leaned into a turn and rolls onto the square corner of the tire, it is losing contact area, and what contact is made is through a harder less tractable rubber compound. Not a good situation considering that as that is happening, the side loading on the tire is increasing as well, increasing the risk of a low side. All it takes is one such accidental drop to wipe out any possible savings you might achieve using car tires on your bike.