Why are procurement much more comfortable running a weighted RFQ than a weighted reverse auction?

The vast majority of procurement departments are familiar with running a tender process with some degree of weighting attached to the quality and commercial aspects. Presumably, and understandably, because you do not buy on price alone. Yet, there seems to be some resistance to apply the same process to run a weighted reverse auction. I'd be keen to hear from those of you who run weighted RFQ's but avoid doing the same for a reverse auction, to understand specifically what the objection is?