Some companies such as BP had all officers living amidships.
One reason for bridge amidships was the belief that large ships could not be 'conned' from down aft.
The main mover to 'all aft' may have been the Stanvac Japan explosion and several other similar incidents around that time ( 1958). A ship that was 'in build' for Stanvac around that time ..Stanvac Horizon.. was completed as 'all aft' while an earlier ship of the same class .. 'Bideford' was built with bridge midships.
The original Finnish owners of the ship here were , I think, amongst the last to build 'bridge midships ships up to about 100,000 dwt.
Another latecomer was the japanese 'Idemitsu Maru'.... largest tanker in the world when built 1966 ... and possibly the only tanker over 200,000 dwt to have a midships bridge.
https://www.relevantsearchscotland.co.uk/ships/ships/066idemitsumaru.html

One of the reasons I heard was that it was also a matter of not mixing deck officers with engine room personnel , they were a different breed of people.apparently .

Why this "bridge amidships" design was used so much for tankers back then instead of single aft superstructure?

Excellent !, this vessel together with her sister must have been one of the last "bridge amidship" tankers