I've flown DL out of EWR many times, and I've never seen the precheck line open - doesn't matter whether it's been at 5:30 am or 5:30 pm. I agree, it's super frustrating - and on top of that, TSA for those gates at EWR seems to have the slowest throughput of any TSA I've been to anywhere in the country. It drives me nuts.
On the positive side, as mentioned above, the newly renovated EWR SkyClub is quite nice and plenty spacious relative to the volume of traffic.