It is evolution. Palm trees are much more related to grasses (and thus cereals), onions, etc., and are monocotyledonts. Monocotyledont means having only one embryonic leaf in the seeds. Other trees are dicotyledont, having two leaves in the seed. Being more closely akin to grass, palms have no growth rings. Pine trees (with multi leaved seeds, and naked ones at that (gymnosperms) are a the evolutionary ancestors of the great European, American and tropical forest hardwoods and other trees with growth rings.
Palm trees transport nutrients all the way up to the top of the tree through all of the tree cells, which grow vertically. Hardwoods transport nutrients up the outside in the new cells and lay boen new cells for transport each season. Thus growth rings.
Thus sayeth the Jim