Actually the 3k/2 mile WR's and close marks over the years have been set by 5k/10k specialists and 1500/5k specialists almost equally.
Just off the top of my head I think of these people:
5k/10k
Puttemans 8:13 WR, 7:35 WR
Viren 8:14? WR
Foster 7:35 WR
Rono 7:32 WR
Mourhit 7:26
Tergat 7:26?
Geb 7:25?
1500/5k
Komen 7:58, 7:20
Saidi-Seif 7:26?
Moorcroft 7:33
Aouita 7:32 WR?
El G 7:23
Morceli 7:25?
My memory is a littel fuzzy and I am not remembering the 2 mile WR's between 8:15 and 8:01 that well, but ceratinly there have been a lot of 5k/10k greats that have run WR's or close to it in the 3k/2 mile over the years. Probably just as many as 1500 types.
And you didn't say this but I don't buy it that the 3000m is not a fiercely contested distance. Everybody runs it from the 1500 runners to the Steeplers to the 10k specialists. Also the quality of the 3k WR is right up there with every other record, even the rarely run 2000m is. Every worlds-greatest almost miler has set a WR in the 2000m: Jazy 4:54?, Walker 4:52, Cram 4:51.XX, Morceli 4:48?, El G 4:44.
And those marks fall right in line with their respective mile/1500 WR's.