To view the possible beginnings of spring festivals, we have to peer back in time. (prehistoric--prehistory--before recorded [written] history) Here is the archaeological record.
Sometime in the last 50,000 to 100,000 years, man learned to control fire and bury his dead. More important was the advent of language. The action of scooping water (for instance) could be enacted by a fallen hunter (perhaps a broken leg in a hunting accident) to express the IDEA that he was thirsty and desirous of a drink. It isn't difficult to imagine grunts and gestures incubating and developing into language. Even today certain people are described as "talking with their hands." But things really begin to reveal themselves 30,000 to 40,000 years ago. Discovery of cave art is evidence that man understood concepts and symbols. Humans display non-linear thinking.
"Thus cave art was thought provoking, and the thoughts it provoked provided the impetus for men and women to lay the foundation of theories of life, and of the universe. Precisely because of its non-material, its metaphysical (beyond the physical) qualities, art became the father of religion." ~ Paul Johnson Art: A New History
I would add a caveat to Johnson's idea: dreams and visionary plants. (hallucinogens)
"The tendency to perceive reality in the terms provided by the SACRED marks a fundamental difference between primitive and modern Western societies, where the distinction has been destroyed. The openness to the world as a sacred reality is probably the most pervasive and common meaning in all forms of primitive religion and is present in definitions of time, space, behaviors and activities." ~Charles Long Primitive Religion
Following the rational for the Sphinx being 9000 to 11,000 years old, we know the reason it points east; the spring equinox. This then, is the genesis for spring festivals: death and resurrection. (i.e. immortality)
Contrary to accepted thought, we have a much longer cultural history than acknowledged. It is time to surrender to what we don't know, or won't believe...
To Be Continued