Tyre manufactures invest large amounts of money in research, engineering and testing of each tyre compound, because they know that tyres are a matter of life and death.
Tyres are the only thing connecting the car to road and they must perform equally well at low and high speed, on a dry or wet surface, on bad roads and uneven surfaces and therefore only the very best materials are used, when producing tyres.
When a tyre ends its useful life on a vehicle, typically only a small percentage of the tyre is actually worn away. Thus the rest of the tyre should be put to good use in new end products. It is a waste of valuable raw materials to either burn them in cement kilns or use them as filling material under roads, where they are only substituting gravel, sand and stones.
ELTs can in fact be a rich source of high-quality raw materials that are only waiting to be recycled and get a new life in a new end product.