I can not, and will not, profess to speak for anyone but myself. I can only recount my position and offer suggestions as to what would have made me participate sooner.
First, the obligatory background. GOTM 19 is my first submission. Which isn't the same as saying that it was my first GOTM. Not at all. I've been playing since about 14 or so. Every month I'd actively snap up the download and have at it. I'd read the chats, I'd follow the strategy - Hell, I'd even follow the 'rules' for when to read one. The thing is, I'd never submit my game. And make no mistake, this wasn't an "Oh, I forgot" or a "I ran out of time." I typically will be done the GOTM a few days after it's come out, such is my CivAddiction. I just would make the cognative choice to not submit it. Why? Easy. I'm a competative guy. I like a challenge. I like contests of wit and strategy. I love to be challenged and have to think my way out of situations I can't get my all-purpose chainsaw in range of. All of that said, I just never saw a point of immasculating myself on such a grand scale. What I mean by that is, say there's a game. And it's a modified map, and it's helluhard, on Deity level. Okay, that's above my normal choice for play, but I'll go along with it. Now, to my way of thinking, I'd rather spend my time worrying about playing so far out of my league, staying competative, and not getting wiped out by the AI before I can get out of the stone age. I'd like to play the game, without having to worry about how I'm going to stack up to people who are inevitably going to get tens of thousands of points. The best I've ever gotten, ironically, is somewhere around three thousand - and that was playing an Emperor game. To me, and myself, that's a great accomplishment for myself. Like, god damned pop the champagne I not only survived an Emperor game but won it. And got my best showing ever against well, myself. Now, I turn around all proud and pleased with myself and submit it. And...gee, I'm somewhere in the middle of the pack. Yay. 97th place. Whee. Suddenly, that enthusiasm has been dealt a crippling blow and I'm going to be over in the corner crying now. Sure, it's admitably hyperbole, but the fact is it's about how I feel. And knowing this going in, knowing that you're incapable (Unwilling?) of scoring above 10K (Nevermind nearish 30K) where's the motivation on my part to participate? Someone the other day tried to do it as a metaphor of the Boston Marathon, but really I disagree with that for one difference. I can play and compare myself against the GOTM faithful without posting, without participating, without talking - and know where I finish in comparison to them. I can't however, tell you how I'd place in the Marathon. And that's where I find the greatest bit of discomfort with the GOTM games. The fact that no matter what I do, no matter how good I am, I'm not going to get 1st place. My philosophy of playing precludes me from going out of my way to maximize my score. My philosophy is to win the game, defeat the AI, and make sure my Civ is the last one standing, and have fun doing it.
I don't know if there's others out there who share this thought, but maybe there are. Again, I can't tell you how to please everyone. I can only suggest what would have made me submit and get into it sooner. As it is, the reason I did submit for 19 was because of the new scoring system and the idea that maybe I didn't get 97th place. (I likely did, I was only concerned with survival, and beating the thing on Emperor just so I could say "Nyah, I did it!"). What I would suggest, as a possible addition, would be the creation of a time-period based tiering. When you release the scoring and standings, you could divide up the results into the various existing categories, and then add a new section where all games ending on a certain date are ranked. For instance, if I (Hypothetically) managed to defeat the computer in 1752AD, then my final score would be placed against all the other games that ended between 1650-1800 (Someone more technically minded would be better for picking the amount of 'turns', I'm just being general). That way, when I get my 97th overall placement and start throwing things - I can seek solace that while my score is divisible by ten of the one who won, I can think to myself that hey at least I got third place in my time-period. That for me, would be the kicker, because then I wouldn't be ashamed of my 97th place finish when measured against those who run the clock down. I could measure against people who had an end around when I managed to. I wouldn't advise the same thing in terms of win conditions though, because those could still be 'milked'.
Something like that would have made me submit my game before now, and that's about all I can recommend. As for being an active poster in the boards, I doubt that would ever happen. I've never been fond of being the outsider, and there's a tangible 'family' and group already established here who can communicate using vowels or strange abbreviations I've no clue about. Familiarity and all that. And that's not an indictment at all for them, I think it'd be great to be one of said group. But from the outside looking in, it's daunting and intimidating. Or well, okay. That's an unfair statement. Such is the way it seems, and often feels. But, that's just mine own thoughtlings on the matter. Hope it helps.