Write-Host strips newline characters where Write-Output does not - powershell

Question

The command $output = Invoke-Expression "cfn-lint *.yaml" gives me an array for $output:
$output.GetType()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True True Object[] System.Array
Write-Output $output gives me this nice output:
Write-Output $output
W2506 Parameter AMIID should be of type [AWS::EC2::Image::Id,
AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>]
trace3-ec2-virtual-machine-creation.yaml:27:3
W2001 Parameter VpcId not used.
trace3-ec2-virtual-machine-creation.yaml:32:3
But Write-Host $output gives me a version with all the newlines stripped out:
Write-Host $output
W2506 Parameter AMIID should be of type [AWS::EC2::Image::Id, AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>] trace3-ec2-virtual-machine-creation.yaml:27:3 W2001 Parameter VpcId not used. trace3-ec2-virtual-machine-creation.yaml:32:3
Why is it doing this?
I know that I can get around this with the call Write-Host ($output | Out-String), but I don't understand why that works.

Answer 1

Write-Output takes [-InputObject] <PSObject[]> as argument while Write-Host takes [[-Object] <Object>] as argument.
Write-Output returns the objects that are submitted as input.
Write-Host sends the objects to the host. It does not return any objects. However, the host displays the objects that Write-Host sends to it.
As you can see, Write-Ouput takes an array of PSObject as Input parameter and returns the same array as Output.
Out-String works fine with Write-Host because it is converting your array to a multiline string hence Write-Host will return it as literal to the Information Stream while without the Out-String it is taking all lines of your array and joining them into a single line string.
PS /> $test = #(
'this is a'
'test'
)
$writeHost = Write-Host -Object $test 6>&1
$writeOutput = Write-Output -Object $test
$writeHost.GetType()
$writeOutput.GetType()
IsPublic IsSerial Name BaseType
-------- -------- ---- --------
True False InformationRecord System.Object
True True Object[] System.Array
Edit
Following your comment, I don't know for sure why, I couldn't find any relevant information on MS Docs for the cmdlet but we can assume it is doing some sort of manipulation on the input objects. We do know that Write-Host is a wrapper for Write-Information.
Take this function as an example, it receives a [object] in this case it receives an array with 2 items as input and writes to the information stream a string representation of it's input:
$test = #(
'this is a'
'test'
)
function TestString ([object]$String) {
Write-Information ([string]$String) -InformationAction Continue
}
PS /> TestString $test
this is a test