The outer grooves have relatively more fidelity (needle moving faster) than the inner grooves, so the master may be progressively tweaked to add more high end as the content gets closer to the inner groove. The closer you get to the inner groove, the lower the playback fidelity.

12" Singles have larger groove spacing so you can slam them way harder than an LP. There is a greater margin of error and less chance of the cutting lathe skipping or hopping during cutting the master.

The process for creating stereo vinyl recordings is pretty much a compromise that allows stereo content while maintaining compatibility with mono playback equipment. This results in another series of compromises/limitations in the mix, like severely limiting the amount of truly stereo content. Extremely loud or bass heavy content that is panned wide would cause the cutting lathe to skip, etc.