Why is RuBisCO enzyme the most abundant enzyme in the world?

The enzyme Ribulose-1 , 5-bisphosphate carhoxylase/oxygenase, most commonly known hy the shorter name RuBisCO is used in the Calvin cycle to catalyse the first major step of carbon fixation.
RuBisCO is thought to be the most abundant protein in the world since it is present in every plant that undergoes photosynthesis and molecular synthesis through the Calvin cycle. It makes about 20-25 % of the soluble protein in leaves and is made on the Earth at the rate of about 1000 kg/s. It is estimated that every person on Earth is supported by about 44 kg of RuBisCO.