…which was Closed two weeks ago, and thus we can no longer discuss its merits there.
Although I am perfectly happy with the PNG format, for myself and my uses, I can understand why someone would have other preferences.
If, as for most of us here, we only use this feature occasionally, the complaint above seems trivial and petty.
But if your work involves picking and exporting hundreds of such frames, for that person it is a big issue.
This is the same basic issue involved in another thread requesting another change, which is so similar that if one is addressed the other should be addressed in the same software fix.
In both cases, it is a small annoyance for some, but a very large problem for others.
My suggestion on this one: Make Default Frame Save Format a Settings choice.