I think it's important to ask questions because there's been literally "dozens" of different things "definitively linked" with CCD. The public likes to seize on neonicotinoids, but they're probably one of the least supported of these many different "definitively linked" reasons. Whole countries have gone so far as to outright ban neonicotinoids, with no effect on CCD. France, for example, banned them. The next year they largely switched to blaming the condition on Asian Hornets when the decline rates didn't decrease.
The problem is that when you ban a certain pesticide, people start using others. And going from neonicotinoids to organophosphates is a massive step backwards in terms of general safety, not just to pollinators, but especially to more complex animals as well. But the biggest problem with the neonicotinoid theory is that neonicotinoids are only used in a small fraction of the areas where CCD exists. Bees can only fly several kilometers from the hive, they're not going cross-country and picking up every pesticide in every farmer's arsenal. It even exists among people who are in places where no pesticides at all are used.
It's easy for the general public to latch onto a particular cause. But once you learn more about beekeeping you realize how incredibly much out there is that can utterly f* up a hive. And which have in history regularly collapsed bee populations, far worse than the collapses we have today. Trachael mites once nearly obliterated beekeeping in Europe, saved mainly by the development of the Buckfast bee. Check out this very inexhaustive list of bee pests and diseases. There's even some really counterintuitive effects in that small levels of some pesticides can actually increase hive survival rates, in that they're deadlier to bee pests like mites than to the bees themselves.
The public also tends to totally understand colony collapse disorder in the first place. Normal winter colony death levels are about 15% in most locations (though where I am it's higher). CCD raised the US average to about 30% at its peak. This is painful and expensive to beekeepers, but it has literally no impact on the ability to sustain bee populations. A new beehive can be started with just a queen and a handful of workers. Hives can be made to produce queens en masse through proper management. Hence people can mail order starter hives, and there's never going to be a threat to the ability to produce these starter hives - a single hive can make many dozens per year. Even normal hives not managed for breeding starter hives will naturally produce several swarms every year; beekeepers try to discourage and/or catch these swarms.
In all likelihood, neonicotinoids are one among many different stressors to bees in the modern era that causes CCD. Modern bees are much more "stressed" than bees in the past. We've created an environment where new bee pests and diseases have spread far and wide to bees that never would have encountered them in the wild. We raise them on corn syrup and sugar water in the winter (good for reducing dysintery and increasing honey yields, but robbing them of certain vitamins and minerals). We transport them on flatbed trucks hundreds or thousands of kilometers (these are animals that get confused if you move their hive a couple meters; their ability to navigate by sight is poor, they're best navigating by the sun and dead reckoning). And countless varieties of poisons, even unintentional ones, affect them every day of their lives. There's so many factors now that weaken hives that any "new" factor to an area can push them over the edge.