I used to be an engineer on Google's search indexing team. I don't have any specific inside information in this case, but knowing the Google mindset, I'm sure

I used to be an engineer on Google's search indexing team. I don't have any specific inside information in this case, but knowing the Google mindset, I'm sure they would have pulled up a large unbiased frequency-weighted sample of search queries with quotes in them. The would have then spun up a custom web search front-end that used an algorithm that sometimes ignored quotes, and ran all of the sampled queries through both the regular front-end and the custom front-end. They then would have manually looked through the affected queries. They would have used this to determine whether the change seemed to better serve the user's intent on average. Of course, this involves a bit of subjective inferring of the user's intent. It don't like it, but I'm sure that for the average query using quotes, it does better find what a user is looking for. That's why Google does this. On the other hand, there's a lot of observation bias: I'm much less likely to notice Google is ignoring quotes when it works out well. It's mostly in the frustrating cases that I really notice and remember noticing that Google sometimes ignores quotes. As for what black magic allows them to sometimes determine that you don't really want quotes, you're guesses would probably be as good as mine. I'm just pretty sure that on average, this black magic has a positive impact on search quality.