When running terraform apply after importing a key pair, terraform wants to destroy (replace) it, why and what does that mean?

I have following terraform config:

resource "aws_key_pair" "default_key_pair" {
  key_name   = "default_key_pair"
  public_key = file("../../public_keys/default_key.pub")
}

Then, I've initially run:

terraform import aws_key_pair.default_key_pair default_key_pair

Followed up by

terraform apply

And it says then that

# aws_key_pair.default_key_pair must be replaced
-/+ resource "aws_key_pair" "default_key_pair" {
      ~ arn             = "arn:aws:ec2:place:id:key-pair/default_key_pair" -> (known after apply)
      ~ fingerprint     = "safasldjfjfljasfjasodjflasjfsdljfasdjf" -> (known after apply)
      ~ id              = "default_key_pair" -> (known after apply)
      + key_name_prefix = (known after apply)
      ~ key_pair_id     = "key-somethin-something" -> (known after apply)
      ~ key_type        = "ed25519" -> (known after apply)
      + public_key      = "ssh-ed25519 SNIP SNIP" # forces replacement
      - tags            = {} -> null
        # (2 unchanged attributes hidden)
    }

What does this mean? I went on with it and definitely the old key pair seems to be working fine. However, looking at the terraform state data I can see that the key_pair_id (I mean the id that looks something like key-0f7664ff3fbd3ed0b) has in deed changed from what it was previously (I had previously ran terraform state rm "aws_key_pair.default_key_pair" && terraform destroy, to shut down the servers while I wasn't actively using them and had taken note of the previous key pair id). So, what exactly happened and why? I would have just expected that after importing the key no changes would be needed to use it.

As per the note from the import section of the documentation for the aws_key_pair resource:

> The AWS API does not include the public key in the response, so terraform apply will attempt to replace the key pair. There is currently no supported workaround for this limitation.