I find this an artificial metric. Normally code just gets split organically as you notice that you can reuse this bit here or that bit there. Some functions won't split and that's OK. (Reference to the 2k-plus-line main interpreter loop in Python.)
Actual reuse is the primary drive for this. Trying to adhere to some other concept instead is dangerous. I've lost countless hours trying to make code "properly object-oriented", or "isolated", or "pythonic" until I realized it's all a delusion.
It wasn't always artificial. When you really were working on a screen that showed 24 lines of 80 characters, it was a good practice to be able to view your entire function at once. That was especially important since at the time we lacked tools like debuggers, and so there was more focus on being able to find bugs by reading.
Today the hardware improvements make those numbers obsolete, but the numbers were picked in the first place because a "screenful" was picked to be a reasonable amount of information to handle at one time -- not just for code, but also for code.
I was never religious about the rule, but it still feels like a good code smell to keep an eye on. If a function gets too big, I start wondering if it's really still doing one thing.
Actual reuse is the primary drive for this. Trying to adhere to some other concept instead is dangerous. I've lost countless hours trying to make code "properly object-oriented", or "isolated", or "pythonic" until I realized it's all a delusion.