Like emski said, it would be useful if you clarified your question. However, I assume you are asking why when you thumbs down a delegate it doesn't reduce the delegate's approval rating by the amount of your stake?
The way DPOS works is that there is only approval voting at the blockchain level. You specify up to 101 delegates with your BTSX balance in a transaction and that BTSX balance is used to support each of the delegates included in that transaction. In other words, there are only upvotes and no downvotes. The reason for this is because of an attack scenario brought up by emski
that was made possible with downvotes.
So what is the purpose of the thumbs down button in the client then? Currently, thumbs down only plays a role if you are voting with your stake using the "Vote as Delegates Recommended" method. Under this method, the slate (a set of up to 101 delegate candidates) published by all of the delegate candidates that you have given a thumbs up to is aggregated together (if the delegate candidate has not published a slate then you can just consider the default slate to be just themselves). The local client can then use these slates to count all the votes in favor of every delegate candidate and rank them in order of approval. If you do not have any thumbs downs, the client will simply take the top 101 delegate candidates in this ranked list it created and vote for them on the blockchain with your BTSX balances. If you do have some thumbs downs for certain delegate candidates, the client will first filter out those specific delegate candidate from that ranked list before taking the top 101 of the modified list and voting for them with your BTSX balances.