Exactly. If the charterer has to pay less fuel for your ship because you put a kite on it, surely they will choose your ship over others? Is there no competition in this market or why does fundamental market principles seemingly not apply?
Additionally if the ship owner was also the operator, they could benefit from some vertical integration, training their crew on the new technology.
If the effect of the kites on prices becomes large enough or the technology becomes standard, expect widespread adoption, but it's a reasonable claim that the existing market structure slows rollout when it's only marginally profitable.
Is that a fair companrison? An owner occupier will often over capitalise because they desire something or have a lifestyle benifit beyond money. A rental owner wil look at dollars in/out. With the ships, its all coming down to a spreadsheet of cost vs benifit for both owner and hirer.
Whats needed is for regulation to come in and say 'ships that have these systems pay less to dock in port' or whatever. But, the technology has to be proven to reduce costs and carbon footprint - so someone needs to make an investment to prove this works before governments will get behind it.