Why isn't post-install script stdout sent to install.log?

Why is install.log on CI so concise?
Try sending post-install output to another logfile

.github/scripts/installer_test.sh

@@ -11,7 +11,7 @@ install() {
         tail -F /var/log/install.log & tail_id=$!
         trap "kill -s TERM $tail_id" EXIT
 
-        installer -pkg $PKG_PATH -target CurrentUserHomeDirectory >/dev/null
+        CI=true installer -pkg $PKG_PATH -target CurrentUserHomeDirectory >/dev/null
     elif [[ "$OSTYPE" == "linux"* ]]; then
         $PKG_PATH -b
     fi

.github/workflows/installers-conda.yml

@@ -293,6 +293,7 @@ jobs:
           if exist %base_prefix%\install.log (
               echo Log output:
               type %base_prefix%\install.log
+              type %base_prefix%\user-post-install.log
           ) else (
               echo No log found at %base_prefix%\install.log
           )

installers-conda/resources/post-install.bat

@@ -1,11 +1,21 @@
 @rem  This script launches Spyder after install
 @echo off
 
+call :redirect 2>&1 > %PREFIX%\user-post-install.log
+
+:redirect
+set
+
 if "%CI%"=="1" set no_launch_spyder=true
 if "%INSTALLER_UNATTENDED%"=="1" set no_launch_spyder=true
+@echo CI = %CI%
+@echo INSTALLER_UNATTENDED = %INSTALLER_UNATTENDED%
+@echo no_launch_spyder = %no_launch_spyder%
 if defined no_launch_spyder (
     @echo Installing in CI or silent mode, do not launch Spyder
     exit /b %errorlevel%
+) else (
+    @echo Launching Spyder after install completed.
 )
 
 set mode=system