Well, while there is no complete documented scope, we can get an idea as follows.
1) Original pitch for the BDSSE which was going to be a new WC like game with drop-in/drop-out coop play and upon completion you would enter the 'verse, a Freelancer style game (but bigger and better). CR said they could do that for a few million and in 2-3 more years, after already having developed a working game, not just a demo (cough, horse manure, cough).
2) Kickstarter goals, where CIG brought the number of systems up to 110, added things like ship modularity, loads of new ships, pets, and more. Actually, not sure how without all these things there was ever going to be a BDSSE, but whatever. CIG then said they would deliver all that for 65 million and no mention about taking more time, in fact they explicity said the expanded scope would not significantly delay the release of features. CR obviously has never read a book on project management in his life.
3) Over 100 episoides of TftC where CR effectively said yes to almost every suggestion from backers, totalling over 1000 times CR said yes, probably, or at worst maybe to expanding the scope further.
4) The 2015 skunkwork project that saw the scope expanded to include full planets and saw CIG focus less on the space aspect of the game and more on the planet aspect. This alone added years (or even decades) of effort to the project, but CIG never directly said to backers how much it had added, how many more years it would take, how much more money they would need.
All of these things increased scope, duration, and money required to levels most backers don't even want to contemplate. While they say they are happy for CIG to take as long as they need, they won't make the logical leap required to understand that to do everything they have promised will literally take decades and with a burn rate of over 50 million per year, they are going to need billions to finish it. Billions of dollars from backers.