Why are Holidays like Easter,Passover,Chanukah etc always in diffrent months/dates every yr?

Differences in calendars and the way the dates are calculated. Passover and Chanukkah are actually fixed dates, the first day of Passover always starts at sundown on Nisan 14 and the first day of Chanukah is always Kislev 25. The date for Easter is based on a formula that takes into consideration the full moons as well as the Spring Equinox and it always falls on a Sunday.

Some use alternative calendars (like the Jewish calendar), while others are set up to occur on a specific day of the week every year, ie: Easter *Monday* or Good *Friday*.

That winds up changing the date they fall on from year to year.