The same reason Christians don't sacrifice animals. Christ was the new covenant. Passover was the old covenant.

In my former circles (highly Dispensational), it was all-the-rage to celebrate all the festivals but with a 'Messianic Jewish' spin. But Dispensationalism is error, so also the fruit from that root. Now the former things (of Moses) have passed away; "with a change in priesthood, comes a change in th...

The passover is all about Jesus! We should be celebrating it. Jesus was like, you guys, this passover thing we do, its all about me. This is my body, this is my blood. The meal teaches the New Convenant. Its a great way to teach your children about Christ and to remember what he did for us.

We Christians don't celebrate Passover because we are Christians. The Passover pointed to Christ. He is its fulfillment, like all the rest of the Law of Moses. It's good to learn how Jesus fulfilled the Law, but we don't want to get close to the first heresy of Judaizing.