I'm no expert and as European I have no horse in this race, but couldn't the lack of a paycheck be actually contributing to the stress and resulting inability to work?
ATCs are responsible for the lives of many in the air and a mistake could result in a disaster and possibly criminal charges.
I read somewhere that designing a new plane would be a financially challenging proposition, with a comparatively small return far down the road.
Plus, it would be a new type and airlines would end up with hybrid fleets, increasing logistics costs (spare parts stocks, retraining of mechanics, pilots who couldn't readily switch between new and old planes and probably more).
In short, not a compelling proposition for anyone involved.
The human preserver.