Does somebody know why there are not due dates for social tasks?...

Currently there are not due dates for social tasks. I've submitted an enhancement request with the reference AN-53404.

Cesar: where can you send and track this kind of enhancement requests?

In the section "Resolved Issues" in the release notes of every Appian version, you can find a list of issues and enhancements with its respective reference code that were solved/implemented in the release.

Thanks.