TPM sum of gene expression data

This question is regarding the ‘CCLE_expression.csv’ file in DepMap Public 22Q2.
When I calculated the sum of the TPM values for each cell-line, I find that 70 cell-lines have the TPM sum <900,000. The lowest value of TPM sum is 662,808. Since the ideal sum of TPM values is ~1000,000, I would like to know if there is a reason why some of the cell-lines have lower sum of the TPM values.