No, it's not "spouting off." Those exit polls are what are routinely
released to various news outlets *during* the polling.

Thats not true. The do not release any of the data to anyone because it
would sway the remaining votes one way.

If it were a matter
of waiting until the polls closed, there'd be little value to an exit poll
since the ballots would soon be counted, anyway.

That's how it worked in the 70's and early 80's, but not today. Today the
exit polls are used after the polls have closed so that they do not have to
wait on all the precincts to report in which can take an hour at the least.
With the exit polls, it allows them to call the state as soon as the polls
close.