Edgar: .312-.418-.515/147 OPS+ B-Ref credits him with 66.4 oWAR. By the way, he was a + dWAR guy in '90. '91 & '94, before he went to DH fulltime in '95.
Chipper: .303-.401-.529/141 OPS+ 87.4 oWAR
Vlad: .318-.379-.553/140 OPS+ 59.3 oWAR B-Ref has him as a -10.7 dWAR guy for his career, almost all in RF. Edgar was -9.7, and most of that at DH.
Thome: .276-.402-.554/147 OPS+ (tied with Edgar for 47th best in MLB history) 77.1 oWAR.
OK, Chipper's oWAR gets him in. That separates him a bit. So do Thome's 612 homers. Vlad was an MVP, but beyond that there isn't anything that separates him from Edgar, other than he played a fairly bad RF. He might have helped his team more as a DH. In his 4 seasons in Anaheim, his only AL experience, the Angels mostly had terrible DH's and went the committee route. Well, Salmon wa good in 244 '06 PA's. They should have played Vlad there, as his glove was sort of sketchy.
From '95 (when Edgar went to DH) until his final season in '04, Seattle's 1B-men were Tino Martinez (1 season), Paul Sorrento (2), David Segui (2) and John Olerud (5). They ran OPS+'s of 135, 121, 123, 119, 102, 117, 136, 146, 107 and 90. Edgar averaged about 160 over that period of time (until his final season in ''04), the other guys averaged 123, up until '04. As it turns out, Sorrento ran a 123 in '97. That was .269-.345-.514 w/31 homers. 11 guys hit 33 homers or more in the AL in '97. 8 guys hit 32 or more in the NL. So there were less than 20 guys that you could use at DH, if the M's didn't have Sorrento and moved Edgar to 1B in '97, who bashed like Sorrento. How many of them could the M's get? Only in Segui's 102 '99 and Olerud's 107 '03 (and 90 OPS+ in '04, when Edgar was basically done, too) can you say that we had 1B guys with weak 1B bats. Even if you stick Edgar at 1B by trading our 1Bmen, it is problematic that you get a better bat at DH than the guys we had playing 1B.
So Edgar gets penalized for playing in the AL and having a bunch of good to real good 1B bats on the M's. Some of those guys were leathery glovesmiths, too.
Edgar helped his team more by playing DH than 1B. And it cost him votes.
Some voters ain't paying attention.