Mahathir was Prime Minister 1981 to 2003. He returned to politics in 2018 out of spite, to dethrone his former protege. Now he's retiring at 94 years old, and threw the Malaysian government into disarray.
Banning sand trade to Singapore is part of bigger elements at play in SE Asian politics. Malaysia's new-old strongman Prime Minister has bigger goals for Malaysia's economic relations with Singapore, and China.