Microsoft has finite resources. Every feature they add comes at the expense of another feature they can't add.
The question isn't "Should Microsoft have implemented VBA on Windows Phone", but rather "What feature should they have not implemented in order to spend time coding, testing and security checking VBA on Windows Phone",
Or if you prefer to use the future tense "Should Microsoft introduce VBA into the next version for the small-ish numbers of people that want it, or should they add something else, like support for older versions of Excel documents?".
That's funny because, again, I'm not talking about wanting support for VBA on the phone. I'm talking about blocking VBA but allowing the spreadsheet to be edited. You are oversimplifying why Microsoft shouldn't work on this feature by making it out to be a much broader scope that the issue presented.