Plane vs Train Security

We took Amtrak up to New York earlier this month and I was struck by the difference in the level of security versus flying

On a plane, you have to show your ID at the counter and your name must match what's on the ticket. Typing to fast online and misspelled your own name? You've got a problem

Your carry on bag goes through an x-ray machine (I'm sure checked luggage has some kind of protocol as well)

You go through a metal detector, maybe get patted down

On a train, I can buy a ticket and pass it along to any bozo I want to, as long as the ticket scans it's all good

Nobody touches my bags

Anyone know why the vast differences between the two travel methods?

What's to stop someone from loading up a bag full of explosives then detonating it?

Probably not a good thing to post on a public message board. But yeah, I don't know the answer to that.