Because they pay lip service? Many people are willing to do that, but are unwilling to make more of a commitment.
They're holiday Christians. They think it'll get them in heaven.
It's a very significant holiday / holyday for us Christians---good sinners and bad sinners alike:
"As we know from the Gospels, Jesus Christ rose from the dead on the third day following his crucifixion, which would be Sunday. His resurrection marks the triumph of good over evil, sin and death. It is the singular event which proves that those who trust in God and accept Christ will be raised from the dead.
Since Easter represents the fulfilment of God's promises to mankind, it is the most important holiday on the Christian calendar."
http://www.catholic.org/clife/lent/easter.php
Love that "good sinners". I'll bet some of the holy types had a laugh at it. :D
The answer to your question? Pascal's Wager. They think that if they put in the occasional appearance that God will think they're one of the flock and, if he proves to be real and not just a myth, occasional attendance will get them through the Pearly Gates.
It's actually insulting because if there actually is a god, they're assuming he's too old and demented to know who was a believer and who was just keeping up appearances
"Christians of Convenience"
While many of the polls will show the majority of Americans are believers, there is very little correlation to that number versus the "Pew poll" (How many actually take part in their beliefs). I happen to like the "Christians of Convenience" since it will be these types that greatly diminish the indoctrination of their young, which will in turn further diminish the next generations involvement, thereby; shrinking religion from within.
They are the salt on the icy foundation of which Americas religions are founded . . .
I've seen just as many sinners go to church on the daily as those "Easter Christians". In fact most of the alcoholics that I've met in church were those who went every Sunday. Hell I've met a couple of preachers who were "friendly" with alcohol. Nothing wrong with that, just pointing it out.
It gives them the feeling that they are Christians, and most doing that think that is what God wants them to do.
Don't assume the term 'sinners' are limited those who do not go to church on a regular or even occassional basis .. Each go to church for their own reasons ... You can not judge anyone by their frequency of going to church .. Because that one guy who occassionally goes to church may very well be less of a sinner than the goomer who goes regularly. Some true believers may choose to not go to church at all because they may believe in God, but they may find the hypocricy of the Church reason to not attend at all.
Because I believe in God does not mean I believe in organized religion. I find it hard to walk into a church that does not recognize my marriage because my husband is divorced. I went yesterday only out of respect for my mother-in-law. She is devotely Catholic and because it means something to her to have her children in church with her.
My guess are their loyalty to God. At this time of the year, the significant of Christ's death and resurrection are on the minds of many people. As a matter of matter, while talking with most people in my community, they love for us to read together the Scriptures in John 3:16 and Romans 5:8. Yes, Easter is a very special holiday for most people.
It does not matter if they go all year or once a year.