^^ You obviously never read about the foiled liquid bomb plots planned by Al Qaeda.
You may not be able to hijack an aircraft with liquids but you can make one go bang with certain types. Terrorism develops and moves on.
In answer to the OP, ICAO annex 17 sets a (fairly low) baseline worldwide standard, national or regional authorities may then set more stringent measures as they wish. Countries like Australia, Canada and the US set quite high standards in their own national programmes. In the EU there is also stricter legislation and then some member states (for example the UK) also choose to add in their own MSMs.