From the import situation of East Africa's overseas oil, it can be seen that if one wants to block East Africa's oil transportation routes, a country would have to simultaneously confine the East African Navy within the Indian Ocean and the South Atlantic off the coast of East Africa. However, it's evident no country can achieve this.
The United Kingdom from the 1980s to the early 21st century could have had the ability to encircle and blockade East Africa on the African continent while the East African Navy was weak. But achieving this might require the full deployment of the Royal Navy. As for why it was after the 1980s, it's because East Africa didn't have a decent navy beforehand.
