The reason the law is worded this way is to make it easy for players, umpires and officials to prevent fake-out style Mankads, whilst still allowing the bowler to run-out the non-striking batsman essentially any time till the ball is bowled.
By changing the wording in the way that is being suggested, you are making the fake-out style Mankad more of a possibility.
Is this a good thing or a bad thing? Who knows. What matters is that the custodians of the game - people who spend their lives studying, administrating and reviewing the laws - felt that a fake-out Mankad is 'just not cricket', and hence worded the law this way. In order for it to change, their views on this topic will need to change.
You can debate this till the cows come home, but it doesn't change the fact that this is why it is this way.
Baseball and stealing bases is a good analogy for cricket. My thoughts are that in baseball there are 4 bases, a run is worth significantly more in cricket, and there are more 'outs' in a game. So the action of stealing a base is both inherently easier and more valuable that a non-striker backing up, and therefore it makes sense to allow for the pitching side to dupe the batting side to steal a base in order to effect an out, whereas that doesn't make sense in Cricket.
The Mankad law as it stands is as good as it's ever been, but it's not perfect. None of the Laws are, and that's why they're constantly revised. I don't think revising it towards allowing bowlers to trick non-striking batsmen into getting Mankaded is the direction the MCC/ICC wants to go.