There is actually quite a few. James Baker III for instance. In fact there is a whole circle around Bush Sr. that kept a big distance from Bush Jr, because of animosity on both sides. Also, all the competent ones probably could see from the start they didn't want to be associated with the Bush Jr. administration.
They are out in force now because Bush Sr. is stepping in to try to salvage the family name. No way of knowing how much or little Bush Jr. wants this, he may be secretly seething or he may have gone to dad asking for help again.
Jay