Azure Devops azure-pipelines.yml template unable to access stageDependencies

Question

I have a stage set up in my build pipeline to detect changes in specific folders in my repo and then I use a condition based on the output variable to trigger or skip a build stage for each path. This works perfectly fine between my Detect and Build stages, but when I then reference a template this variable no longer is accessible.
Code example:

#azure-pipelines.yml file
stages:
  - stage: DetectChanges
    displayName: Detect Changes
    jobs:
      - job: DetectChanges
        displayName: 'Detect changes'
        steps:
          - powershell: |
              $pathfilters = @("ui/", "api/", "publicapi/")
              foreach($path in $pathfilters) {
                $changed = $(git diff HEAD HEAD~ --name-only $path)
                if ($changed.count -gt 0) {
                  echo  "$($changed.count) change$(if ($changed.count -gt 1) {echo s}) detected on $path"
                  echo "##vso[task.setvariable variable=$($path.Substring(0,$path.Length-1))_changed;isOutput=true]true"
                }
                else {
                  echo "No changes detected on $path"
                  echo "##vso[task.setvariable variable=$($path.Substring(0,$path.Length-1))_changed;isOutput=true]false"
                }
              }
            name: detect_changes
            displayName: Detect Changes
  - stage: Build
    displayName: Build
    jobs:
    - job: UIBuild
      displayName: UI-Build
      condition: eq(stageDependencies.DetectChanges.DetectChanges.outputs['detect_changes.ui_changed'], 'true')
      steps:
      - task: PowerShell@2
        inputs:
          targetType: 'inline'
          script: 'Write-Host "UI-Build"'

The above code works perfectly. I output a variable in my DetectChanges stage that I then reference in my build stage for each of my paths(only have one of the 3 placeholder builds in the example above).

The problem comes in my next stages where I have a template defined:

#azure-pipelines.yml next stage snippet (after the code above)
      - stage: DevDeploy
    displayName: Dev Deploy
    dependsOn: Build
    variables:
    - group: dev
    jobs:
    - template: templates/deploy.yml

This references my template with the below code:

#templates/deploy.yml snippet
- deployment: ui
  condition: eq(stageDependencies.DetectChanges.DetectChanges.outputs['detect_changes.ui_changed'], 'true')
  environment: '$(myEnv)'
  strategy:
    runOnce:
      deploy:
        steps:
        - template: uideploy.yml

This stage then is always skipped due to the stageDependencies reference being null when executed from the template.
Stage execution results below show the value as null:

Started: Today at 3:39 PM
Duration: 1h 37m 22s
Evaluating: eq(stageDependencies['DetectChanges']['DetectChanges']['outputs'] 
['detect_changes.ui_changed'], 'true')
Expanded: eq(Null, 'true')
Result: False

Why does running a stage in a template vs in line on the same file result in a variable reference not working?