Of course the pros didn't want discs. Chris Froome is one of the few riders with enough recognition and money in the bank to be able to state the obvious.
As other posters have indicated, it is not just the insurmountable disadvantage of couple of extra pounds of ballast (at the worst place on the bike: the wheels), but it is the glacial race-ending wheel changes, and the constant rub-rub-rub and squeal. What I don't think has been mentioned is the extra bulking up of the frame and fork required by discs, leading to more weight and a less compliant, less comfortable fork. With rim brakes, much of the braking forces gets transferred through the rim into the fork crown, which is already very strong. With discs, all of the braking forces end at the hub, and then through the fork, which has to be reinforced.
Another consideration is the peloton pile-up potential with discs. I'm sure every rider individually wants the most powerful brakes possible (up to the adhesion limit between the tires and the road), but do you really want the guys you'll be drafting for 3,000 miles to have instantaneous skid-inducing braking? And pros weigh 140 pounds and know how to descend and to corner. Does a pro need the hardware of weekend warrior who is carrying 100 pounds extra?
The pros are paid to use what the sponsors drop on them, and praise it no matter what. Even if it is a blatant equipment deficiency, it always becomes rider failure. Pros are essentially paid to sell stuff, which is banks, lotteries, etc, and bike stuff. The target audience of the bike biz is a dentist with a gold card, who grew up mountain biking. Hence road bikes have sloping top tubes, thru-axles and discs. Give the consumer what he wants.
I will admit that road discs have been a boon to the industry. It renders 'obsolete' everything on a bike including all legacy frames and wheels. Complete reset. Further, it sends your average dentist with a gold card to their shop at least couple times per year. Whereas replacing worn rim brake pads is trivial for even someone with limited mechanical skills, disc brake setup, particularly hydraulics is a bridge too far for most home mechanics.