You can't force Tour riders to go to the Duaphine if they have no interest or intent on racing it. You have riders who much prefer other races to warm up for the Tour than the Duaphine. Also even the Duaphine WILL have non Tour riders in it as teams are not going to be sending their full Tour teams to it and there will be non Tour teams at it as well.The problem isn't related to the country one is racing. The problem is racing and mixing with people outside of the Tour bubble. Racing the Dauphine is controllable and good. Racing Strade Bianche, MSR and the Nationals is not; there will be too many non-Tour related people involved. If more races are needed, then add some warm-up races that involve only the World and same Pro Teams as the Tour.
No need to scrap the Tour, everyone just needs to be more creative in the lead-up. They (UCI, ASO and the teams) have more than 3 months to prepare, so it shouldn't be too difficult to get it right. But if they mess up the Tour, THEN the whole season will be lost.
Also different riders need and want different build ups. One size most definitely does NOT fit all and you cannot intentionally harm riders by forcing that one them.
The reality is it's nothing more than a prayer they even race the Tour in the first place. Technically it's best to look at it as the entire season IS lost now. Alejandro has already said he doesn't actually expect to race at all this year.