Why do we not measure FID but the gradient recalled echo?

[dokahashi]

I had a similar question in my MRI physics class and with a friend but neither were really able to help me understand. If the initial 90 pulse in a spin echo sequence produces a FID that, according to the MRI in Practice book, is too fast, how can GRE sequences use flip angles less than 90 but measure those signals?

I am very green and have only been learning this for 5 weeks.