Amplify vs S3: Why is this behaviour different?

HI All, I'm still very much a novice with AWS and I'm following this tutorial to learn more Build a Serverless Web Application. In my own test account I've followed this tutorial without issue. I'm currently trying to apply the same tutorial in a restricted environment where I don't have access to Amplify. I figured I could get away with swapping Amplify in this tutorial S3, however I'm getting some odd behaviour.

• Amplify hosted site
• S3 hosted site

I'm using this github repo website for both. I'm creating the bucket and uploading the files via TF.

resource "aws_s3_bucket" "mrw-example-bucket" {
  bucket = "mrw-example"

  tags = {
    Name = "mrw-example"
  }
}
resource "aws_s3_bucket_acl" "mrw-example-bucket-acl" {
  bucket = aws_s3_bucket.mrw-example-bucket.id
  acl    = "public-read"
}

resource "aws_s3_bucket_website_configuration" "mrw-example-bucket-website-config" {
  bucket = aws_s3_bucket.mrw-example-bucket.id

  index_document {
    suffix = "index.html"
  }

  error_document {
    key = "error.html"
  }
}

resource "aws_s3_bucket_public_access_block" "mrw-example-bucket-pab" {
  bucket = aws_s3_bucket.mrw-example-bucket.id

  block_public_acls   = false
  block_public_policy = false
}

resource "aws_s3_bucket_policy" "mrw-example-bucket-policy" {
  bucket = aws_s3_bucket.mrw-example-bucket.id
  policy = file("policy.json")
}

resource "aws_s3_bucket_cors_configuration" "mrw-example-cors-config" {
  bucket = aws_s3_bucket.mrw-example-bucket.id

  cors_rule {
    allowed_headers = ["*"]
    allowed_methods = ["PUT", "POST", "GET"]
    allowed_origins = ["*"]
    max_age_seconds = 3000
  }
}

###WEBSITE FILES###
locals {
  content_type_map = {
    html        = "text/html",
    js          = "application/javascript",
    css         = "text/css",
    svg         = "image/svg+xml",
    jpg         = "image/jpeg",
    ico         = "image/x-icon",
    png         = "image/png",
    gif         = "image/gif",
    pdf         = "application/pdf"
  }
}

resource "aws_s3_object" "mrw-example-bucket-objects" {
  for_each = fileset("website/", "**/*.*")
  bucket   = aws_s3_bucket.mrw-example-bucket.id
  key      = each.value
  source   = "website/${each.value}"
  etag     = filemd5("website/${each.value}")
  content_type  = lookup(local.content_type_map, regex("\\.(?P<extension>[A-Za-z0-9]+)$", each.value).extension, "application/octet-stream")
}

My question to you all, is why is the behaviour different? It feels like I've missed something obvious somewhere.