As pools grow, the total number of shares per pool grows, and the SP of the pool grows with it. So your vote might still be 2%, but it is 2% of a larger pool. If your share count had not increased, it's likely that your upvote weight would have dropped to 1%

Because rule adjustments are still done manually, we round upvote weights to the nearest unit (1%, 2%, etc) so the adjustments can feel a little choppy sometimes.