Because the "smart money" investors don't want to be discriminated against in the market and they are big enough market participants that they write the rules.

Because the "smart money" investors don't want to be discriminated against in the market and they are big enough market participants that they write the rules. If we did put a name attached to every trade, it'd become clear when someone is breaking up a big order into many small ones to avoid 'disrupting the market price' -- that is, getting a good price for at least some of their sale. Or buy order, I suppose.