Because it's all about cost. Those 400m container ships are ran by a low cost crew of 15-25 with some 3rd party maintenance personnel sprinkled in. Try fitting

Because it's all about cost. Those 400m container ships are ran by a low cost crew of 15-25 with some 3rd party maintenance personnel sprinkled in. Try fitting a more expensive fuel and more maintenance into that. On top of all safety concerns. For ocean crossing vessels they are more closely looking at e-fuels and hydrogen since that gives the same benefitd at cheaper cost with not a too large change in the shore side infrastructure.