It was time and times which were the issue. Britain modernised its forces from 1958 and by extension the Commonwealth did likewise from the same time period. Rhodesia declared UDI before it was completed there (1964), so you end up with SLRs, L7 Brens, FN MAGs and the like for the small regular force and SMLEs, .303 Brens (plus a massive stock of .303 ammo) and Stens for everyone else.
They had Ferrets but never received any Saracens or Saladins (presuming they were supposed to get them at all that is) and Bedford troop carriers. 'Regional defence' was the Rhodesian (and previously the 'Union') mission, so heavy equipment was not envisaged originally by Commonwealth planners.
With South Africa being its main supplier (who also had suffered a British embargo and was forced to look elsewhere), it had to use what they used/loaned/sold and subject to their political whims. So R1 & R1HB, more MAGs... Eland armoured cars and Alouettes.
The Bedford RL was the artillery tractor for the 25pdr originally, so logically the Crocodile was needed as the MAPV when they needed to move around when things got worse.