Why won't Gradle subproject upgrade?-CodePudding

I have the following existing structure

repo
|--orchestration
   |--build.gradle
   |--settings.gradle
   |--gradle
   |  |--7.5.1
   |--engine
   |  |--build.gradle
   |  |--gradle
   |  |  |--6.7.1
   |--process
   |  |--build.gradle
   |  |--gradle
   |  |  |--6.1.1
   |  |  |--7.4

furthermore

orchestration % which gradle
/opt/homebrew/bin/gradle
orchestration % gradle --version
------------------------------------------------------------
Gradle 7.5.1
------------------------------------------------------------
orchestration % ./gradlew --version
------------------------------------------------------------
Gradle 7.5.1
------------------------------------------------------------
cd engine
engine % ./gradlew --version
------------------------------------------------------------
Gradle 6.7.1
------------------------------------------------------------
cd ../process 
process % ./gradlew --version
------------------------------------------------------------
Gradle 6.1.1
------------------------------------------------------------

Now, The Problem

process % gradle wrapper --gradle-version 7.5.1

FAILURE: Build failed with an exception.

* What went wrong:
Task 'wrapper' not found in project ':process'.

cd ../engine
engine % gradle wrapper --gradle-version 7.5.1

FAILURE: Build failed with an exception.

* What went wrong:
Task 'wrapper' not found in project ':engine'.

What is going on?

why was I able to upgrade sub-projects in the past?
why does Gradle so often give unhelpful diagnostics?
- often misleading, where I waste hours on a wild goose chase...
I ran with --scan... after much time investigating... still no insight...
- https://scans.gradle.com/s/xfw6fihozkkem
- but, I did fix two deprecation issues