As more and more delegations are incoming, the % upvote is periodically recast. This way, the % upvote is maintained to almost never go below 90%.
So, the prior % was according to 800k SP but since then, over 1 Mil is present thus more delegators needing upvotes.
So, for your 50k SP delegation it gets 75%. A 10k SP delegation is now 15% upvote but will also be recast as more delegators come.