Known users have an advantage because it's easier for people to find our profiles to check out our memes:
-by clicking the link from the weekly or Top User leaderboard
-by knowing our username to type in to the broswer
-by following a meme or comment we already have on the front page back to our profile
The effect of this traffic is that a meme by a well-known user is likely to get upvotes and comments that other memes submitted at the same time by unknown users don't get. This means that most of our memes get into the top pages of Hot, to at least be seen (not 100%, but most).
And since the majority of people on imgflip spend their time upvoting and commenting in Hot, once our a meme of ours is visible in Hot, it gives that meme momentum to get more upvotes.
If people spent more time in Latest, we'd see more variety of memes, and lesser-known users would have more of a chance to have their memes seen.
(You can still get a meme on the front page even if you're completely unknown if enough people see it. There are plenty of memes on the front page by users who aren't known. But it's harder than it is for a known user, because it's not as easy for unknown users to get their memes seen.)