Spoke with a trucker about this very issue. He started out driving CoE trucks and said when there's a crash the driver is ejected out through the window. Now this was before the days of airbags but that would be enough to discourage their use. He said it got so drivers refused to work at companies who used them. However it was the desire for increased fuel economy that finally ended their reign.

I've no doubt that the old CoE trucks from the 60s were death traps. But I'd be interested in seeing what the difference is between a modern European Volvo (one of the few companies who build both types) and a US version. I would be very surprised if the difference wasn't negligible. Putting the engine out front is a brute force way of providing safety which isn't necessary with modern design.

Maybe dumb question- I've never been in a truck. Wouldn't the distance from seat to window be ~pretty much the same whether it's CoE or conventional?

There's a hood in front of you for conventional, and I guess crumple zone deceleration comes in to play there? But as this article mentioned US trucks have a much higher average/top speed so you're probably just as likely to go through the window.

No safety belts?

This. However... Might help if you drive your semi into a brick wall at speed. Just because you are more likely the truck goes through the wall before the cab does. Which happens, someone drove a semi into a data center of ours. Fortunately DR response included this type is disaster.