Once you become aware of it - ie Broomrape in general - you see it much more often! Common Broomrape is quite common really, and I usually spot it a couple of times a year just while out on a walk. It's even come up once or twice in a flowerbed in my garden, though I'm not sure quite what it was parasitising there. It's frequently mistaken for an orchid, as also is common toothwort.

It seems it just has very long-lived seeds which sit there in the soil waiting for the right conditions.