Your comparing 3 forklifts from different manufacturers all with different load capacity's.
24 volt - 1.3 ton
36 volt - 1.5 ton
48 volt - 2.0 ton

Its easier to make the battery higher capacity & in turn more heavy which in turn keeps the counterweight smaller, this helps to keep the chassis as small as possible as that is basically what 3 wheel counterbalances are all about - manoeuvrability in tight spaces.