One thing I have read repeatedly is that the HoF voters often look for "that defining moment" (ie, highlight reel) on the field during the big game. Swan and Stallworth definitely had theirs.. how many times have you seen Swan's over the shoulder catch as he's going down in against the Cowrhoids in the 1979 SB? Plenty. Monk didn't really have any of those. For that matter, neither did Steve Largent that I can remember. All I remember about him was (like Monk), he caught everything that came his way. Those two guys had very similar careers, with one major difference. Monk has rings. But Largent's in. As SportsCurmudgeon pointed out, Monk was not exactly a press friendly person and they're the ones doing the voting.
I do think the voters' need of wanting the one defining "picture perfect play" along with a career long body of consistent work is a crime. Pure unadulterated bullshit, actually. Unfortunately, I also think that if Monk had retired when his Skins career was over, he may have gotten in already. With Jerry Rice (hands down, best receiver ever) coming through at the end of Monks career and just annihilating all the records like he has, it's probably not hard to put on the blinders and compare everyone from here on out to Jerry. That is damn unfair, just like all shooting guards will always be compared to Jordan. You could be incredible, but compared to those transcendental types of players, you're not going to look like the best.
As far as DG getting in, he'll be a first ballot inductee. Hell, even Dr Z said he's a lock. I've even seem him referred to as the second greatest corner (don't dare say who was the best) to ever play the game by a HoF voter.
I'm pretty sure he has a few highlight reel performances of Mr. Green that'll get played over and over again on ESPN when he gets in!