While the banding ability was never actually removed from the game, no cards have been printed that use the ability in any set following sixth edition and it has never appeared on any rules summary I've seen from the past several years. Why is this? I've heard it's because the ability was 'too complicated'. What exactly was so complicated about it that might have encouraged its extinction? What is a good situation/example that demonstrates why it was probably exiled from the game?
Take it from the horse's mouth:
Banding was an ability that was flavorful and simple enough in the simple cases. But when you left the simple cases and got into more unusual situations, the rules suddenly became very complex, unintuitive, and opaque. You wind up with a mechanic that cannot be understood or accurately applied simply by reading the text on the card and applying your general rules knowledge. Instead, you have to know a whole bunch of banding-specific rulings, and hope you have a copy of the comp rules handy if it ever comes up.
And all of this complexity is maintained for a mechanic that rarely actually mattered. I could be wrong, but I don't believe there is any card with banding that has ever been a tournament staple. Under these conditions, the best choice is the one that Wizards made, which is to let banding lay fallow and pretend the whole thing never happened.
The current official reminder text for Banding is as follows:
Yes, it's taken them 20 years to distil the "simple explanation" of Banding into that - and I bet you still can't tell what it means without reading it slowly and carefully at least three times.
Wizards has made it a bit of a rule of thumb, for quite a few years now, to remove complexity from the game where it isn't needed. Could the game survive with Banding, Phasing, interrupts and mana burn still in it? Almost certainly. Is it better off without them? Again, almost certainly.
The real nail in Banding's coffin is that you can get a similar flavour out of a much simpler rule. Take for example the en-Kor ability from Stronghold:
This does almost everything Banding did - gives the owner some power to control how damage is assigned to his creatures. But with the great advantage of not causing your head to explode while trying to calculate how it works in complicated situations!
I still don't get the difficulty. I don't know if this was just our house rule back in the day or if it was explicitly stated but everyone I knew back in Alpha and Beta days unless all creatures in a band contained a keyword ability then any who had that keyword lost it for the duration of the band.
So in the examples provided, the creatures with trample and first strike lost those abilities the instant they were added to the band. Also once the band is declared it lasts until the end of the turn, so if you take out the only creature with banding in a band the band remains.
The one complexity that existed which could have been completely removed by a rules update was it working differently on attack and defense, just make it so that they are the same requiring all creatures in a band but 1 to have banding regardless of whether you are attacking or defending.