Speak for yourself lol. I'm just messing with you, got to have a sense of humour <-- is that the canadian spelling lol . BTW the greeks are merely a label for a mathematical representation, and with experience you'll realize they don't work all the time, just like technical and fundamental analysis. But you're a vendor, ya gotta sell something...
In my 15 years in the financial markets, I learned few things. But I definitely don't pretend to know everything. I'm still learning something new every day, and I will continue doing so.
No, Greeks don't tell the whole story. But they can guide you in the right direction. You just used them by yourself by mentioning the <6% probability. How did you reach the 6%? By looking at the delta.
Look at it this way: yes, it is only 6% probability. But it means that in 6% of the trades, it will (or might) happen. If you collected $2 credit on a $10 spread, and it is worth now 0.30, why not to close it? You originally risked $800 to make $200, but now you risk $970 to make an extra $30. Is it worth it? Not to me.
Yes, price action might support that the spread will expire worthless, but many things are beyond our control. There are geopolitical risks - what if tomorrow Trump bombs North Korea and the markets crash 20%?
Closing early have another advantage: you release the margin and can use it for the next trade. And the next trade has (hopefully) a better potential then the extra 2-3% gain that you are holding for.