Aside from the additional costs involved in purchasing, installing and maintaining these footrests, believe it or not there is an additional expense for the fuel involved in carrying the extra weight around. I would have thought it would be negligable really but the airlines have used this as reason for removing other inflight amenities (ie; phones). Also, TWA installed footrests on all of their a/c at one time - not too long ago either (in the early-mid 90's) and took them out after not too long. I don't recall why but it apparently just didn't work for them.