The short answer is that because different or new isn't always better. Modern materials like composites have pluses and minuses compared to metal or wood. One

The short answer is that because different or new isn't always better. Modern materials like composites have pluses and minuses compared to metal or wood. One of the huge minuses is repairability and structural strength for long spans. Solar power for propulsion works for small vehicles, but not well for larger ones where energy density is important. Or on cloudy days and at night. In the boating world weight is less of an issue, but in aviation composites often end up weighing more than aluminum, especially in the first batch. They also have temperature issues over about 300 mph, compared to Mach 2+ for aluminum. It sounds like this boat restoration was ill-advised, but that really depends on their long-term goals.