If you want a coal-related motive, try the obvious: Pennsylvania is an important swing state. Mines are hiring again, for both miners and engineers.
The Emma Maersk carries 11000 TEUs on every voyage, so the amount of solar panels that will be installed worldwide in 2018 is about 6 shiploads.
What about the future, when photovoltaic becomes the dominant source of marketed energy? According to the IEO, current total world marketed energy consumption is 20 terawatts (20'000 gigawatts), which would amount to about 90 million TEUs, or 8000 shiploads. Call it 30000 shiploads to account for photovoltaic's low capacity factor, typically in the 20%–30% range (though we can expect that to become more efficient as development moves to more equatorial areas with less clouds).
There are currently about 9000 container ships in operation, so current world marketed energy consumption is about three trips for the world's shipping fleet, in the form of photovoltaic panels.
Total container shipping volume is already about 470 million TEUs per year: https://en.wikipedia.org/wiki/Container_ship#Container_ports
We can presumably expect panels to become smaller and lighter as time goes on, further decreasing the energy needed for shipping, and eventually the proliferation of solar panels will depress the price of energy so low that not even bunker fuel can compete with syngas, at which point the bunker fuel emissions problem will be over.
(Edited to correct order-of-magnitude calculation error.)
If that is the case, why would this not work for cargo ships as well?
Ship screws, on the other hand, can be designed to run at nearly any speed at all, and nearly all the time the ship is moving at exactly the same speed. So the screws are just coupled directly to the crankshaft of a two-stroke diesel engine the size of a fucking church which remains powered on for years at a time, always running at whatever speed it damn well pleases.