Game development times are getting completely out of hand at this point. I really hoped that the advancement of game creation technology and more advanced engines, we would have seen sped up game development, but for the past decade we've seen nothing but the opposite go the point it's just ridiculous now for some games.
This also poses the other question - who thought it was a good idea to show an ES6 teaser if the game was the better part of a decade out at the time of the teaser?
Showing off the teaser was a good PR move in my opinion, because they played it right after they announced some ES mobile game. Same year Blizzard did the same with Diablo Immortal without mentioning Diablo 4 and we all know the "Do You Guys Not Have Phones?" meme that produced
This one isn't due to extended game development time really. They showed an ES6 teaser (just the logo really) at the same time they announced Starfield in 2018. They had just started working on Starfield at that time and had no plans to start ES6 until it was done. That's about now, ~5 years later. Expect ES6 to be out in 5-6 years, which is in-line with previous BGS games.