Pods are used primarily for manoverability. This allows Cruise ships to get in and out of ports with a minimum of assistance (none at all, if conditions permit). This is important because they are entering and leaving ports every day or two. It also makes sense as the hotel loads on these floating skyscrapers is similar to the propulsion loads so having combined main engines and generators gives other advantages.

Ocean going container vessels on the other hand use massive direct drive two stroke diesel engines (usually they only have a single engine). They have no gearbox. The only way to go-astern is to literally start the engine in reverse. This can only be done up to a limited speed, otherwise the windmilling effect of the water passing through the prop would overpower the starting air.

Suffice to say, I'd put a long bet on the overwhelming majority of containerships being powered by internal combustion engines in 30 years time. If we get our act together we might have come up with an alternative / synthetic fuel by then but I wouldn't hold my breath.