Adding blocking between joist to support column?
This is the reason for the blocking:

&quot;additional vertical members (2x4's) to carry the load from the beam
up to another load bearing object above the floor (e.g. a new column)&quot;

In other words, it's a complete load path from the beam to the foundation

if it's the later, what's benefit using the block to support the
column? wouldn't be better for the column to go straight down through
the subfloor and rest directly on the existing beam?

Depends on what you mean by better.
Better related to the load path? Yes, in that all the pieces will be imperfect and have a little gap between them that has to close up before the load is applied. Note that wood has more strength along the grain so install the wood blocking vertically, not horizontally as most other blocking.
Better related to buildability and cost? No. It is done this way for a reason. It is much easier and therefore faster and keeps costs down.
This is an extremely common detail and if you're architect and engineer are doing their job correctly, then there are no issues.