If you've piled up wins and have purposely not moved up in division thinking you'll always have easy matchups, that's no longer the case. The matchmaking system looks at your number of wins first and foremost. So if you have thousands of wins and are still in Silver when you're clearly good enough to be a Gold, Platinum, or even Diamond, you'll pull tougher matchups.
People don't like tougher matchups, so they block them. That works. Sort of.
If you block too many teams, the matchup generator will have no choice but to grab a Pro team for you to face because you might have blocked everybody within your range of wins... and the odds of them being my Giants or the Marlins are pretty darn slim.
I don't really worry about my roster until all my upgrades are maxed out, then I look at players. I find multi-drafts to be the best value because you'll at least get one good player, and anybody I don't need I'll just trade in to level dudes up.