It seems that ponies have an acutely short term memory unless they have something specifically pointed out.
This applies to lessons learned, personal traits of other ponies they know, or even their own personal natures (loyalty, generosity, etc.).
I was thinking this back from the first season, where we had the Mane Six that had saved the town and even all of Equestria multiple times, yet even the ponies in their own small town they lived in didn't even seem to notice them, much less treat them as the heroes they were. The Elements of Harmony, ponies. Come on. :-)
Then there was quite a series of episodes where one or another of the Mane Six had to relearn something fundamental to their own nature that they already learned in a prior episode even.
And little things like this, where anypony knows shouting at and stressing Fluttershy isn't going to do anything productive. Or a very recent episode starting with Dash pranking Fluttershy, yet back in season one, Griffon the Brush Off, both Pinkie and Dash herself agreed you can't prank Fluttershy because even their most harmless one would hurt her feelings.
So just accept that ponies have a long term memory issue and are going to repeat many of the things they learned.
Probably why they don't have prisons and such and generally forgive ponies if they just apologize (even if you imprisoned and enslaved the entire town), as nopony is probably going to even be thinking of it in a week from then. :-)