the hype is around the game being good, not the game being engaging for a long time. its like hype over a book by a famous writer - even if the book is short its the want to see their new content that justifies/results in the hype.
tlou is just one of those rare games/potential series that has very engaging storytelling, quality gameplay, excellent aesthetic and atmosphere that makes it have all this hype around it. people really are just looking forward to more of the same (quality) so imo its not excessive hype thats unfounded.