While you may argue that abandoned software is "abandonware," FarSight Studios still owns the rights to the original code. Furthermore, distributing the ROMs of Williams tables (which contain copyrighted code from the 1990s) is technically a violation of the Digital Millennium Copyright Act (DMCA).
In the official version of Pinball Arcade, tables were locked behind in-app purchases (IAPs). You could buy "Pro Packs" for individual tables or seasons. In the version circulating for V2.22.19, the OBB file has been modified to bypass the license server check. The result: Pinball Arcade V2.22.19 -All Unlocked OBB- -Latest-
Risks specific to Pinball Arcade