Eurotunnel's system is very nice, but only works for a short journey: they don't provide space on those trains for passengers to relax, you stay in or near your car. This is perfect for 30 minutes, also makes faster loading/unloading, but can't work for longer journeys. Also because of this "stay near your car" thing, their trains are wider than usual trains in Europe, which makes it impossible for them to go anywhere except on that dedicated tunnel.
I'd love to see a solution that actually works almost like them but for longer trips: there is zero fun driving 1000km by the road when you need to go somewhere. It could be fun if you have time, but otherwise it's boring and tiring, would much prefer driving at the destination than on the journey.
The lorry drivers do have a separate cabin that they travel in. The cars are in completely enclosed double-decker carriages, but the lorries are open to the elements.
Less open to the elements now.[1] The lorries now ride Eurotunnel in cars with a solid roof and steel truss sides. The roof is to prevent projecting objects such as antennas from contacting the overhead power line (that's happened) and the open sides are to allow fire extinguishing (that's happened, more than once.)
Such are the practical problems of a "rolling highway" Eurotunnel has had to solve.