Why do some Bible translations leave out certain verses?

They're not hiding anything—modern translations are usually more transparent about manuscript evidence than older ones were, not less.

Older translations like the King James Version were based on a set of Greek manuscripts assembled in the 1500s. Since then, scholars have found much older manuscripts—some over a thousand years earlier—that don't include a handful of verses those later manuscripts added, like part of the ending of Mark's Gospel or a line added to the Lord's Prayer. Most modern translations still print the well-known passages, but bracketed or footnoted, explaining exactly what the earliest evidence shows.

That's not deletion. It's telling you more, not less, about how confident scholars can be in a given verse—so you can weigh the evidence yourself instead of receiving no information about it at all.

None of the passages affected by this changes a core Christian teaching. Doctrines sometimes connected to a disputed verse rest on many other, unaffected passages throughout the Bible.