I think riders should generally make an effort to go to the World Championships. It’s an important race and if you stand a chance with the parcours or could be key in helping your team, you should go. If a rider is very fatigued and out of peak shape it makes sense to not go, but that should be the exception rather than the norm.
There may need to be some sort of incentives to help bring in more of the top riders. Prestige comes down to quality of the field in cycling, so having the best field year in and year out is also the best way to incentivize riders to enter.
Don't know how long you have been following cycling, but it was Armstrong who started snubbing Worlds, when he would have been selected by his national team. It was a poor example to follow and has done a disservice to cycling. It thus has nothing to do with the parcours, in this sense, but respect for the race (and, yes, I still think that should mean something for reasons already stated in previous posts). When Pantani was chosen for Italy, he went, no questions asked, which obviously wasn't going to be on a course for Cipollini. The point is that here Pog goes, Van Aert goes, Remco goes (with the exception of Van Aert, is the course any more suited to the others than Jonas and, if so, by how much? I mean it's not a 1980 Sallances or 1995 Diutama mountain goat's parcourse), while Johnas has been called up by Denmark, but refused to go. The Tour winner isn't going to represent his flag, but the runner up is, and the reason stated is lack of motivation (for Worlds?). Perhaps my expectations are just anchored in a past that is gone and unfortunately never coming back, but I can't approve of the Tour winner not showing up for this Worlds. And if the Worlds has gone to the Land Down Under, on the other side of the globe, twice in the last 12 years, well it's clearly an indication of how much, second only to Europe, Australia contributes to cycling's base development and financial stability. The Aussie fans thus deserved to have the Yellow Jersey amongst the field of contenders at the elite mens road race riding for the rainbow stripes.