I think it is probably because that most people think that if the record is over, you have to get up and change the record, or turn the system off, anyway. This thinking is okay, as long as you don't fall asleep during listening. if you tend to fall asleep, then there are at least 2 models that I know of called "The Lift" that can be put on just about any manual turntable. They have a high, and low price model, both under $100. Simple, stick-on installation. It seems to be a copy of the old Monitor Audio arm lifter from the 1970s. I believe it is available through Expressimo Audio website.
Why Not Semi-Automatic Style Turntables?
It strikes me as odd that there are few (if any) high-end turntables that lift the stylus (tonearm) off the record at the end of play. Is this really that hard to do without compromising performance? It seems to me that some sort of infered sensor could determine when the tone arm has wandered far towards center, and a mechanically decoupled bar lift the tonearm off the record. Is something like this out there, and if not why? Is it really impossible to do this without compromising performance, or are turntable designers stuck with their own blinders?