Tracks don't analyze on import?

I have a USB drive that I dropped a bunch of tracks onto its collection, directly from the file explorer without importing into the main collection. When I was playing later, I realized that most of them were not analyzed, but some of them were. What determines when EP auto-analyzes tracks?

I am finding the same thing but I am not too bothered, I just analyse them after. Perhaps it bypasses analysing them to speed up transfer.