The reason that has never changed is because of how it affects the senior pilots who normally run unions (or pilot associations).

Payscales are skewed to favor senior pilots, that's obvious.

The current pay for block, but not duty also favors senior pilots if you think about it...

Look at two trips:

1. 5 Legs, 8 hours block, with 4 hours of non-block duty time (pre/post duties, turns, swaps, airport appreciation) for a 12 hour duty day.

2. 2 legs, 8 hours block, with 1.5 hours non-block duty time for 9.5 hours duty.

Which trip is going to go more senior?

#2 of course, because it is easier, shorter day, and pays more per duty hour.

Here's the kicker: Any realistic scheme to change pilot hourly pay from block to duty is going to require a reduction in hourly rates across the board. This will effectively take money away from the senior guys who hold sweet high block/duty ratio trips. Since senior guys run the union, it's just not one of their priorities. Personally, I'm all for it.

Rigs can prevent truly unjust block/duty ratios at the bottom end, but they aren't going to provide as good of a deal as simply bidding for trip #2.