Guessing... 5.6 or newer? Searches more than a couple of days old?
What happens with the newer database is that if the data is older than a certain timeframe (date/size), it's not in our "hot" storage, which is unpacked and ready for searching. When we have to go back to "warm" (somewhat compressed) or even "cold" (further down the rabbit hole), things have to be unpacked before you can read them. You're effectively decompressing compressed data, then searching the decompressed data. I'm sure the initial decompression does take some cost as data is shuffled.
On very new searches, I don't think there would be as many writes.
Yeah, after thinking about how that works it started to make sense to me why I would see more writes than reads, initially it's just very counter intuitive.