You are missing a key piece of the puzzle. Your vote worth isn’t based on the price of steem it is based on the portion your vote takes up from the reward pool.
As more people exercise their voting power, your vote is worth less. That’s why when someone posts for $500 10x a day it is a big deal.
You're right, it's something I did not know, so it's not an official modification, it's caused by that. It seems that then we are having many posts every day with very high values. In any case, it is something that is affecting us all. Thanks for the clarification.