I don’t want to say for sure, but most likely it is something technique related. The only thing related to a bow being worn, would have to do with not as many hairs being on the bow as before (you lose them over time). This can lead to a weaker sound, but not a bad sound. There is a lot that can be said about right hand technique; are you self-teaching yourself or do you have a teacher? I find that students that self-teach themselves can actually get worse sound over time if they aren’t holding the bow properly, and applying the proper muscles with the index. If you are interested in creating a clear sound across the strings, I highly recommend watching this intermediate violin lesson.