You’re ignoring:

Problem is, what is the tradeoff. So you switch to driverless trains. First of all, it has only worked in completely isolated systems until now (no mainline railways). Then, you have the problem that when something goes wrong, the consequences in terms of delays are much larger, often making the news, because there’s no one there that can just “quickly do something” to get around the problem and keep going. People tend to get stuck in trains for long times when issues arise - see the REM in Montreal. What’s the consequence of unreliable public transit? People tend to avoid it more, often switching back to their cars for important trips - a much more dangerous form of transportation.