Sforno on Exodus 13:4/ספורנו על שמות י״ג:ד׳

1בחודש האביב, the reason that the Passover festival is to be observed in spring is so that it will coincide with the legislation of marking the lunar new year with the month of spring, the month of rejuvenation. Our sages have been very careful when calculating a permanent calendar to ensure that Passover never occurs before the spring equinox.