Why aren't rifle bores hard chrome plated like shotgun barrels, to prevent corrosion and ease the cleaning?

One reason is in rifles the accuracy isn't as good as barrel that isn't chromed. Another is the addition cost. I'm not sure but I believe some shotgun barrels are.

As said, the accuracy is supposed to be less, slightly less so some sell on that. Friend had a Mauser in .270 WCF from post WW II Belgium with a chromed barrel. When the accuracy got past 3/4 inch he sold it and regretted it ever since. It came with a chromed barrel. Many AR's are chrome lined barrels for rust resistance and slightly longer life, accuracy diminished for volume of fire. Happy Trails.