There are many reasons as to why king tut’s tomb was the greatest discovery. The most important is that it was almost left intact. Though it was believed to be robbed, it was still left with most of its artifacts. There are only two known pharaoh tombs that have escaped tomb robbers—king tut’s and Psusennes I.
The second reason is that King Tut was believed to be the son of Akhenaten. His father created a radical change in Egypt and it is believed his son tried to restore Egypt to its old ways for fear of retaliation.
Third reason, Tut’s tomb was built in a time when Egypt was at its finest in art and religion. In fact, if king tut was in fact the son of Akhenaten, then his depictions should be closely related to his image. (The art of his time I believe was from the Amarna Period. )
Forth Reason, King tut was just a child when he acquired the throne and died at a young age. It is believed his tomb treasures might have been put together at the last minute.
Fifth reason, king tut’s tomb reveals a lot about Ancient Egyptian pharaohs and the culture of the time.
I hope this helps a bit! I know it was a quick response but I think it is enough to get you on your way!