The only reason they won't change it though is because they do not want to give the referees and disgression in calling the call. By not making it a judgement call in any way shape or form, it makes it impossible to change the rule. That makes it an even worse rule in my mind, but the rules committee did feel it was a bad rule, but it is so rigid that it was impossible to alter without changing the rule entirely.
Let's face it. The Brady tuck rule play (and the one that Testeverde had against the Patriots earlier that season) the QB had no intention of throwing the ball and was in the process of tucking the ball back in, but hadn't completed the motion. If the ref had the ability to apply judgement in that case, it probably would have been ruled a fumble because Brady pretty clearly was not going to throw the ball. We got away with one because the rule as it was. It happens every week in the NFL.
The Emmitt Smith rule is a bad rule, but it is still a rule. That rule where David Patten recovered a fumble while unconscious, but happened to be touching the ball while he laid part in bounds and part out of bounds is still a rule. It is a rule that if you fumble the ball on the other teams' one yard line and it fumbles out of bounds through the endzone, it is a touchback and loss of possession eventhough if it bounced out two inches shorter prior to the endzone, the offense would have maintained possession of the ball. There are just a lot of bad rules in the NFL.
I do disagree that the only way to get rid of the tuck rule is to get rid of the arm moving forward rule. There are plenty of ways to revise the rule. Many of them require judgement calls
There are a lot of bad rules in the NFL. Just because it is difficult or impossible to change them without impacting that and other rules, doesn't make it a bad rule. Sometimes the rule is bad, but better than not having a rule in at all.