Why doesn't the NBA credit assists on made free throws?

Rondo got robbed of an assist when Garnett got hit.
Rajon Rondo's spectacular streak of 30 games with 10+ assists has led me to keep a very close eye on his ball distribution of late.  As he continues to climb his way up the charts towards the all-time record, I watch each game intently keeping track of his assist count.

While at the Garden last Wednesday I noticed three or four occasions where Rondo found guys open at the rim, only to lose out on an assist because KG, Sullinger, or Chris Wilcox got fouled and missed the layup.  And that got me wondering, why is this the case?

The fact that his teammates were fouled doesn't make Rondo's passes any less valuable.  If the player still makes the free throws, and the points still go on the board, why shouldn't the passer still get credited for the assist?  And if the shooter makes one of two* foul shots, why not award half an assist on the play?  Obviously changing the rule now would make it impossible to compare records, but shouldn't it have always just been this way?

* And on the very rare occasions when there is a potential assist on 3 free throws, I still think it should be .5 if one is made, and 1 assist if either two or three are made; it's not like you get a "bigger assist" when a player makes a 3 pointer anyway.

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