The Flynn effect documents an increase in IQ, but does not say there will be a consistent 2.93 point increase --- in fact, the increase is not consistent, but rather concentrates in areas of lower socioeconomic status.
Kids eat better and we focus way more on both their early development and schooling then before. Why would be better results so surprising?
yes it seems mostly to be from the nutrition aspect as IQ is supposedly supposed to be immutable otherwise
That's not true. It is definitely not settled that IQ is believed by scientists to be immutable, and, in fact, a widely held hypothesis for the increase (shared by Flynn himself) is that the cognitive environment has become increasing complex, which is having the effect of "training" higher IQ.