They cared enough to keep searching for my keywords, to click on my ads, but then they realized they were not interested and bounced?
Also, like I said, the traffic the ads generated was good (it generated prospects fitting the profile I was targeting, and I was happy with the numbers), so yes, the ads were effective.
My point is, either the traffic got worse or your ad is no longer effective and a higher bounce rate can indicate either. Bots don't shoulder aside regular users, so regardless of whether there are more bots, there are less users. Otherwise you'd have seen traffic increasing but not conversion. If traffic is flat and interaction is down, you've lost interested users and you need to look at your creative, or your targeting, or possibly consider whether any design or content changes on your landing page could be responsible. It could also be that you are getting outbid and your placement is now not catching the best customers. The fact that what worked before doesn't work now is totally normal. Customer tastes change, competitor behavior changes, the traffic supplier is changing. Ad buying is a constant battle.
Also, like I said, the traffic the ads generated was good (it generated prospects fitting the profile I was targeting, and I was happy with the numbers), so yes, the ads were effective.