Same with Montenegro. The road does not make economic sense, either for Montenegro itself, or for a connection between Belgrade and Bar. The demand that would justify building and maintenance of such a behemoth in the wildest Balkan mountains just isn't there.
If the region was flat, there would have been a (much cheaper) highway a long time ago, but it isn't. It is an engineering hell, much like most construction tasks in the mountains.
Heck, even California dropped its plans for a bullet train from SF to LA because it was too expensive to cross the mountain ranges that stand in the way. And California is orders of magnitude richer than Montenegro.
Mountains are best avoided when building roads. If you absolutely can't, the viability of the project needs a long, hard look.
https://en.wikipedia.org/wiki/Hambantota_International_Port
Or at the highway in Montenegro, a small and poorish Balkan country that cannot really afford a $1 bn project going through the worst mountainous terrain in Europe.
https://www.npr.org/2021/06/28/1010832606/road-deal-with-chi...
This kind of bad investments tend to be signed by corrupt politicians and sometimes backfire spectacularly.