I do have a very old post that used to be rather popular here that listed various restrictions related to compression. One of the most obvious restrictions in older versions was that the basic / OLTP (Advanced Row) heap table compression based on symbol tables / de-duplication was limited to tables with 254 columns or less - or probably more general to rows with single row pieces.
This limitation was lifted with Oracle 12c which started to support this compression type with tables having more than 254 columns / multiple row pieces - and there is a new internal parameter called "_widetab_comp_enabled" that defaults to TRUE.