Because it takes time.

I'll have to release a new version with updated codes that make Whatsapp think we are using latest S40 version, so maybe some of the errors reported above are solved.

coderus and others are writing libwa, which would unify all the different versions that are out there, and in an ideal world, yappari would be ported to use libwa instead of its own code.

Now, that would take quite a lot of time and effort, so it's not a question of being a technical imposibility but of man-hours.