My point being, if you can see a tornado coming, you'll have ample time to take shelter in a basement [or if you're in an unpopulated area, you can get out of the way]. Why people get killed by tornados "still" is usually insufficient shelter (homes without basements or safe rooms), quick touchdowns, them occurring at odd hours when people are sleeping, or the occasional goliath tornado with a massive damage track that's moving quickly, in the wrong direction.
I've also experienced being caught in the middle of a tornado outbreak (30 in 90 minutes, a couple were over mile wide) while driving across southern Minnesota. We sheltered at a Walmart and were quite alarmed that no locals seemed to take it seriously, even when the roof partially lifted off and cars started getting tossed around in the parking lot.
IIRC the State recently switched to more localized warnings (not county wide) due to people ignoring the sirens.
I'm also pretty sure that "you can see tornadoes coming" is poor advice, especially since they often come at night or with significant rainfall.