Foreign leaders exchange official visits to strengthen bilateral relationship as platform for cooperation. From thereon, it evolves into business, investment, cultural, education and various people to people social and economic exchanges.
Mahathir could be envious or jealous because no Saudi Arabian King made an official visit or undertake any major investment or donation during his 22 years premiership.
Most likely, Mahathir knows the the official visit to Malaysia would vindicate Dato Najib from the allegations made against him.
It was Mahathir who orchestrated the political assasination with people he used to dub as enemy of the state. He sparked the 1MDB debt problem.
Mahathir will need to get his not-so-maestro media spinners to discredit and nit pick issues on Aramco's RM31 billion investment in Pengerang's RAPID.