Why don't some GOP candidates drop out of the race ?

If you were able to gather a minimum of $120,000 from your supporters a day, or even a week, through emails, would you drop out?

It's about the money, honey, and the dillusion that they might get lucky and win a state

Probably because poll numbers don't mean shit. 68% of voters say they haven't decided on a candidate yet and nobody has voted.

You're suggesting they throw in the towel before the first bell has rang.

They'll probably start dropping off after Iowa.

$$$

By not dropping out and having your private handlers fund you Trump is kept from the 50% threshold needed for the nomination.
However this will end shortly. The handwriting is on the wall.

TRUMP 2016

Kasich, Christie, Fiorina and Rand will drop out after a couple of states. Their support will shift mostly to Rubio.

Rubio will jump into the #2 position, and start whittling away at Trump's lead. If Jeb drops out early enough, his supporters will go overwhelmingly to Rubio, as he is the closest to an establishment candidate which is Jeb's only base.

The establishment will then gel behind Rubio while Cruz starts to wither away. Rubio knows this, which is why he suddenly turned evangelical in the past debate (Cruz's base).

Carson will hang on way too long, and his supporters are the key. Who knows who they'll support.

Trump does not have the wide open lane yet.