This program is software under the GNU Affero General Public License, version 3. Anyone using it over a network is entitled to its complete source code; that entitlement is met by this download, which is built from disk when requested, so it is the code this server is running at that moment rather than a snapshot of what it once was. It carries the program's own code and its licence file, and never the database — birth data belongs to the people it describes and is not part of any source release.
Why this licence. Not by preference — by inheritance. The calculations use the Swiss Ephemeris, published by Astrodienst AG under either the AGPL or a paid professional licence. Taking the free edition means the AGPL applies to the whole work. That is a fair trade and it is met in full.
The method is not licensed at all. The Table of Ascendants chain, the ephemeris interpolation, the classical rules — these are centuries old and belong to the tradition. What is licensed here is one arrangement of Python, and nothing about the knowledge it implements.