People in the comments of this video said that Whitebeard realized that Luffy was the next Roger and that’s why he supported him. The real reason is that Oda and Whitebeard realized that nobody but Luffy could get past Garp. Garp is on the same level as Roger and Whitebeard. Garp is also in good health unlike Whitebeard who was sick and injured. He one shot Marco and Burgess. He could have easily killed Whitebeard if he felt like it. Akainu would have learned what real absolute justice looked like if he didn’t listen to Sengoku. Dragon and Shanks are the only people that could maybe beat Garp.