With Uncharted 4: A Thief’s End set to be Naughty Dog’s final game in the franchise, Creative Director Neil Druckmann told the New York Times that part of the reason he returned to Uncharted was to end Drake’s adventures:

It’s time. Sometimes, a character just lets you know it’s time to move on. For me, that was part of the intrigue of coming back to this world. You never see something successful in the industry end. It usually just fizzles out.

After Druckmann revealed that the game’s story changed “100%” from Amy Hennig’s original vision, Game Director Bruce Straley revealed just how hard Naughty Dog is working to finish Uncharted 4:

This is the biggest, most ambitious Uncharted ? let alone game ? that Naughty Dog has ever endeavored to take on. We want to do this justice. We want it to be a mind-blowing, eye-popping, sweaty-palms adventure. Everybody is bleeding out of their eye sockets to make it come together. We want to make sure Drake is sent off properly.
If you missed it in the recent story trailer, Uncharted 4 will flash back to when the two brothers were young. “As they go further, we’ll explore their differences,” Druckmann added.

#ff follow newly revealed Uncharted 4 actors: @ChaseAustin1093 (young Sam) @Warren_Kole (Rafe) @Robin_A_Downes (""") https://t.co/wqYVkFbHBC
? Neil Druckmann (@Neil_Druckmann) February 26, 2016

Naughty Dog also showed off some old concept art ...