Where have all the Travel Bugs gone?

During our North Carolina vacation I was astonished to find that 90% of the caches that indicated in the inventory that there was at least one travel bug present had none! Where have all the travel bugs gone? Are they being held by geocachers who wait extended periods to log them? Are they being stolen by anti-geocaching nuts? There are a few of them out there. The last two summers that I was in the North Carolina it seemed much different. The inventories were pretty accurate. Now they aren't. I've checked back numerous times on several of the TB Hotels I've visited and found that the inventory indicates they are full but the TBs aren't there. Usually I've been able to take back to Ecuador a good number of TBs and coins that have as a goal to travel the world. This time in a month of caching I've only gotten two to take with me and place in one of two TB Hotels in Quito that serve as a great launching point to Europe or back to the US.