Technology

I think the mixing being different is likely dependent upon how good the engineer and mastering engineers are/were. I'd wager a fair number of bands releasing their albums to vinyl these days simply send over a very similar final master (maybe slightly less loud if you are lucky) to the vinyl cutting without much thought, because it's the hip thing to do.

You are accurate, that they should ensure that low frequencies are mono compatible, but it is likely less of an issue for the style of music most associated with vinyl releases (indi etc), as stylistically they don't tend to use stereo widening on low frequency instruments. Generally they have kick and bass down the center channel, or I suppose going mono style out of L/R if they are trying to be really old school, but that would likely take a completely different mix adding to production budget as I can't imagine if would work to well on phones etc, which a lof of music is mix for unfortunately.

None of the artists I produce or mix for have requested it yet, but if they did I would send them to Fuller Sound Mastering as Michael has been around for ages and knows how to handle masters for vinyl.

Vinyl cutting also has an EQ curve offset that is printed into the vinyl itself, cutting the bass and boosting the high frequency, which is then re-applied by the players preamp circuitry, I believe it's referred to as pre and de-emphasis. Funny enough my mastering DAC actually has this feature for some kind of old early CD technology for some lower resolution digital formats that had issues with noise and filtering and used a similar technology, I had never heard of this until I purchased this particular unit haha.

I agree that some cases are brittle but I've not seen a disc get fucked since I was a kid, when I couldn't be bothered to put them back in the case.