Why? Does not the Notre Dame worth the cost?????

For me is very useful!
And the Space Elevator too!
Maybe I am still a rookie...sigh!
This was pre-BtS when the Notre Dame only gave 1 happiness per city, not two. Now I actually need it in some cases.
The Space elevator, though... One has to notice that the 50% build bonus is additive, like any other %-bonuses. So if you want to build Casings, for example, with Forge, Factory, Power, Laboratory and State property and w/Aluminium and your base prod is, say, 50, the actual prod is (25+50+50+10+100%)*50 = 117.5. With Space elevator it's just another 50% more, then the prod is 142.5, which is 24% increase. It isn't much, really... Especially in Ironworks city (Ironworks adds another 100% with coal). Just two, maybe three turns less.
Besides...
I wouldn't otherwise have to research robotics and that stuff, I'd prefer teching fiber optics and fusion meanwhile I build my other spaceship parts.
SE costs 2000 hammers, five times more than one SS Casing. With all the hammers wasted on the SE, you could easily have built all the casings!
Besides, there's the latitude rule, which limits the # of cities SE can be built.