Here are my thoughts on why there would never have premium processing on I-140.
About 2 years ago or so when there was no AC21 law and you had to have your I-140 and I-485 approved to be able to change your job legally or stay in this country legally. During this time, the approval of I-140 used to be anywhere between 2 weeks to 6 weeks (mostly), and I-485 used to take more than a year to be approved. So the time it used to take for a applicant who has labor certification was around 14 months or more.
Once AC 21 law came into effect, the processing times of I-140 became slowly creped upto 6 months or more. And since applying for I-140 and I-485 concurrently was not allowed, you needed to wait for about 6 months for I-140 approval, then apply for I-485 and wait for another 6 months to be in a safe position.
After this, they approved a law (or whatever), that would allow a person to concurrently apply for I-140 and I-485 once the labor was certified. Once this came into effect, the I-140 approval timings have slowly creped up to 14 months or so.
If you look at the above three scenarios, the time that a person has to wait to be safe once their labor has been certified has not changed much. If they start the premium processing for I-140 applications, then they would be drastically changing the situation by which an applicant can concurrently apply for I-140 and I-485 and be safe in 6 months once they have a certified labor. Why would they want to do that?
So the moral of the story is that we should not except the processing of our IMMIGRATION Related Applications any sooner then they used to be a few years ago.. Always assume that you would have to wait longer than what then your predecessors.
These are my thought only and I would really be happy for the next generation of Immigrants if the situation of this immgration process changes even slightly in their favor.
-Godse