The naming of the celebration as “Easter” seems to go back to the name of a pre-Christian goddess in England, Eostre, who was celebrated at beginning of spring.
Easter is quite similar to other major holidays like Christmas and Halloween, which have evolved over the last 200 years or so. In all of these holidays, Christian and non-Christian (pagan) elements have continued to blend together.
I am a religious studies scholar specializing in early Christianity, and my research shows that this dating of Easter goes back to the complicated origins of this holiday and how it has evolved over the centuries.