Where do you save transistors? With the Posit you have to be able to deal with larger mantissa, multiplier size scales with mantissa bits squared, so even a small increase makes quite a mark.

Maybe you save a bit by not having denormals, but then parsing the packed float is a bit more complicated in that the bits do not have a fixed division between exponent and mantissa.

It is possible that the Posit circuit was smaller by leaving out some feature, like exact rounding, which is quite expensive, but then it is not an apples-to-apples comparison.