From the Bitcoin Core developer notes, when the bash script is included in the commit message the "Travis CI job checks that the result of the script is identical to the commit." It also makes it more efficient to review for reviewers if they can review and run a bash script rather than needing to do additional checks that the PR covers all the cases it should.
With regards to the scripted-diff examples looking complicated you can look through other examples in the Bitcoin Core repo by running:
git log --grep="-BEGIN VERIFY SCRIPT-"
Alternatively here is a simpler example that you can start from if you are trying to do a basic find and replace exercise.
For more information on scripted-diffs see Jon Atack's personal notes on scripted-diffs.
If you need help writing your bash script you can ask questions on #bitcoin-core-pr-reviews on IRC.