The loudness and compression on Low's last couple of albums is very much deliberate, so it's surprising that the vinyl doesn't have it. Though I heard similar claims about Sleater-Kinney's The Woods, which was also intensely compressed for artistic effect.
The reason it was backed off for the vinyl master is most likely due to physical limitations of the medium. If the audio channels are too loud (wide) there is risk that the needle will jump out of the groove.
There's compression and distortion for sure on the vinyl, but when you look at the waveform on the digital it's right up to the max. It completely changes the sound.
The thing is, vinyl (and tape) typically can't reproduce waveforms like that accurately, so it's difficult to compare. You can take a hyper-compressed master, cut it to vinyl or record it to tape, then play it back in to a computer, and it'll look different and less "brickwalled".
I dunno if you’ve listened to these records in question but it’s very, very obviously for artistic effect. They’ve discussed it in interviews and stuff. Low wasn’t looking to get radio play with fractured collages of distorted noise. The “vinyl can’t reliably reproduce these waveforms” explanation someone else suggested makes the most sense.