I think its a tough question to really answer.
why was he popular, because Vince McMahon made him popular and Hogan was smart enough and politically astute enough to ride that until he basically miscalculated and became a caricature of what made him popular
I mean he had all of the natural personality traits, he was smart enough to know that he had to do things that invited audience participation, he looked out at the audience, he hulked up with audience participation, he was the king of the catch phrase littered promo. But he was a boy band, he was a creation of Vince's and at the same time he was also a creation of a massive push. The wrestling audiences weren't as smart back then, so it was easy to push Hogan as a larger then life good guy against cartoonish bad guys. Vince also was smart enough to create over whelming odds and monsters to feed Hogan thus making him look like the greatest thing since sliced bread.
He was also a poor worker who leveraged his clout to make himself look amazing in every match. His charisma is awesome his back stage politicking and clout always made him the top of the show at the cost of whatever company he was with.
I think if you talk to most wrestlers that aren't in his circle of sucks ups and friends, they will say that he did great things in terms of bringing attention to the wrestling business in the 80's and early 90's, but he crushed more wrestlers and wrecked more companies then anyone else. I doubt that anyone outside of his circle of suck ups would even be bothered to cross the street to help him if his house was on fire.
When fans started getting smarter in the 90's fans and the attitude era hit, Hogan really couldn't adjust and he basically became a running joke as a Champion, put on even worse joke matches and utterly crushed anyone to protect himself, when he said he put over younger guys, he basically crushed then and made then look stupid and then basically rolled over on his back.
He really should have walked away from the business in about 96 instead he over saw the downfall of WCW with his backstage antics. Then went to TNA and used his enormous ego and backstage precence to get his friends their last big paydays while crushing the company under his boot.
You ask me why he was so popular, it was because Vince McMahon hit lightning in the bottle and decided that the business wasn't about Wrestling, it was about larger then life entertainment and Hogan could do that. At this height in WCW he rode one event as long as he could and then boosted himself on the fallen bodies of other wrestlers to keep his spot. By the time he hit TNA all of his charisma couldn't make him interesting or the company relevant.