As I said, the main reason is that every feature has to start at minus 100 points. It's not that your idea is bad, it's that it has to be sufficiently good to warrant the risks that come with any code churn, no matter how small. "Simple and obvious" does not mean "easy and risk free". I'll admit, aside from the performance concerns, this would be a relatively easy change; but "relatively easy" and "relatively safe" still means "using resources that could go towards other features" and "potentially dangerous".

For debugging, you always have the option of wrapping the broken code in try/except and logging the values you're interested in (with or without reraising). If you believe that's insufficient, please, submit a patch (with tests), or find someone who is willing to do so. Otherwise, you have to accept that other people don't always share your beliefs about what is worth their time to improve; telling them they're wrong for disagreeing doesn't help.