Why has no one except Bakugo figured out that All Might passed his powers to Deku?
Bakugo wasnt the only one to notice similarities between Midoriya and All Might. 
Asui pointed out when they were traveling in a bus that Midoriya quirk was like All Might's in season 1 episode 9. Later in season 2 episode 10, before fighting with Midoriya , Shoto Todoroki told Midoriya than since his father was Endeavor who wanted to defeat All Might, if Midoriya had something from All Might (One for All?) he had more reasons to defeat him. The difference between them and Bakugo are


As pointed in another answer, Midoriya told Bakugo he received his powers from someone else
Bakugo noticed the enemy of All Might was All for One who had the hability to transfer quirks. 
Bakugo knew All Might met Midoriya (who was quirkless at the time) (and him) when he was captured by a monster in episode 2 or 3 of the first season. After that Midoriya started to show All Might's powers. 
Bakugo saw that Midoriya was crying when All Might consumed all his powers and said "Now is your turn" to the camera. 


So in conclusion Bakugo and several others noticed similarities between Midoriya and All Might, but only Bakugo was exposed to additional information who made him conclude with almost certainty that All Might transfered his powers to Midoriya