First, it already goes into the receiver's catch rate -- it's just that fans pay less attention to stats like those.
Second, by your logic, a QB shouldn't get credit for passing yards if he just chucks it up and the receiver outjumps two defenders, or dumps it off to a guy who breaks a tackle and runs 30 yards after the catch -- after all, those positive plays were blatantly created by the receiver. It injects far too much subjectivity into record-keeping if a human has to dissect every play to assign credit and blame. Who gets credit if it's a great throw and a great catch? Who gets credit if it's a mediocre throw and a bad catch, but still complete? What if it's a great throw but the receiver ran the wrong route and it gets picked? What if it's a bad pass AND gets deflected off the receiver's hands for an interception (see: the Unga interception)? What if the QB leads the receiver directly into the path of an oncoming defender (arguably what happened on the McBride INT)? If we don't even trust NFL officials to consistently call what's a catch and what's pass interference and what's holding, why would we trust them to know each player's responsibility and assign blame subjectively? The potential for added controversy is just staggering.
Third, it's not like there's any tangible consequence of having an INT assigned to you. A turnover is a turnover. Coaches can already grade players based on their actual performance, and observers simply have to be smart enough to consider context when looking at any number. The only people this matters to are fantasy football owners and ignorant fans who talk smack about stat lines without watching the games.
