Why some filters works with transparent background and others don´t ?

I have seen that using some filters with a image with transparent background (Alpha Channel) shows the result right and it keeps well the same transparent background and what is more important for this thread and question, these filters does NOT have any Get Alpha/Set Alpha components to make them compatible with alpha channels.

Then other filters are not compatible with a transparent background as it is all filled with a solid color or filled with the filter effect, and to be able to make them compatible and keep the alpha channel it needs to be modified as shown very well by CFandM in this thread here

So I wonder why some filters keep well the alpha channel from the source and others filter do not and fill it all?

I think that maybe is because the components used, and there may be some components that when using them they do not work with alpha channels and so they need to be added the Get Alpha/Set Alpha combo, this may be like the seamless tiling that is incompatible with some components.

SOME FILTERS COMPATIBLE WITH ALPHA CHANNEL (without having Get Alpha/Set Alpha combo)

Fake Buzz by Gene S Morgan

Trangliar Pixel Painter by jffe

Silver Surfer 1b by Kraellin

Polygon Painting by Vladimir Golovin

And then most of the other filters that I have tried do NOT work with alpha channels unless they have specifically built-in alpha channel compatibility made by the author of the filter and most usually the filters do not have this included.

On some filters is not possible to simply use the CFandM tip shown here and needs a more complex solution as happened with this Sketchy Painting Alpha by emme that kindly was done by emme

On some filters because the way they work and the effect they make are not possible to keep the alpha channel and if possible would need much more work than just adding the Get Alpha/Set Alpha combo and possibly rebuild the filter again