[Lordstan]

Mantle's popularity is really not that difficult to understand.
1) Played in New York.
2) When He played in NY, the team went through an amazing run of success. Because of this he got national exposure doing heroic things on the biggest stage.
3) Good Looking
4) He was on the team that STAYED in NY after the Giants and Dodgers both abandoned the town.
5) Because the others left, there was no one in NY to share the spotlight with until 1969, when the Mets won the WS and he retired.
6) He was generally thought of as a good guy who liked to have fun. (Much like Bill Clinton. A party boy who women loved and men wanted to be). The Charisma factor.
7) He was pleasant with the media and fans unlike Mays, Williams and Dimaggio.
8) He was on the show circuit for almost 20yrs prior to passing away. During that time, he was great with fans. Don't underestimate the impact this had. People have truckloads of stories of Mays, Dimaggio and Williams acting surly and sometimes downright rude to fans lining up to pay them to sign their name. Certainly this soured many of those who saw those two as heroes. Mantle was 100% the opposite. He could be fall down drunk and would give you a perfect signature, smile at you, and shake your hand.
9) He was a classic hero story. Someone of immense talent who suffered yet still overcame. Now some of the suffering was his own doing, but almost everyone who saw him play before the knee injury felt he could have been even better. Who doesn't love the aw shucks guy who is given a bad break but still finds a way to succeed? Sounds like about a bazillion movies I have seen.

PS: Despite the Mantle could have been better if he didn't hurt his knee argument, there is no doubt in my mind that Mays was a better ballplayer. The reason I say this is that Mays had the handicap of playing in San Fransisco for all those years. He probably lost 5 hr a year to the stupid wind of Candlestick. If you add 5hr x 10yrs(1958-1968) brings him from 660 to 710hr. Who knows, maybe playing in Polo grounds and it's short LF porch gets him 10 more per year. Maybe he challenges the Babe and gets the accolades for breaking that record. Now you add in all the other numbers and it makes it an even stronger case.
Mays is not, and will never be, as popular in part because of being black at that time in our history, but also because he played in SF, and not NY, before the internet and other media would level the playing field. Additionally, there is almost no one who doesn't think he is a nasty human being. He was not particularly fan friendly when he played and in the 1980's on the show circuit he did noting to change that perception. Hard to be someone's hero if they think you're a prick.