Because that is just part of various longer processes, for which the computer would be a lot more patient, accurate and (if reliably programmed) quicker than I.
I am processing a lot of spoken word audio (hours’ and hours’ worth) — which needs to be cleaned, breath by breath, click by click.
Sometimes, I must be prepared to scale back or undo parts of the “cleaning” where unrequired or too severe.
For example, a debreath plug-in sometimes mistakes intentional sounds — parts of words — for breaths; or else ignores real breaths.
When I step in to reduce the breath by hand, I might want to keep a copy of the the original raw sound in case I have to revert.
At that point, manually, I would do as you suggest - copy, enter, down-arrow, enter, paste, enter, up-arrow, enter, then run the effect, select the next problem, and so on.
Believe me, to be able to do this with a single keystroke could knock hours off my workload.
I have a series of denoising routines I run on a raw file before processing, and another series I run after processing.
In each case, and for each track, I make a duplicate for posterity before working on it.
(I have been caught out before by Audacity crashes, and it’s not funny when a two hour audio piece becomes unrecoverable).
Again, if I could automate the taking of duplicates and running of strings of effects into one Macro, I could leave each processing, go and put the kettle on — over time, yet more hours saved.
But, when things are duplicated, or copied and pasted, Audacity tends to maintain selection of both the new pasting and the original copy; thus any effect run automatically, as a step in a macro, operates upon both the original and the copy.
So again, if there is a macro step by which to deselect the original (or else the copy) before proceding, I want to know about it.
I could go on. Suffice to say, I have many batch processing uses to which I could put this new Macro facility — but I’m falling at the first hurdle because I can’t find a macro step for selecting and/or deselecting from the currently focused track.