Why seaplanes became high-speed test aircraft

Why were seaplanes used as high-speed test aircraft despite the drag of their floats?

Open water provided much more room for takeoff, landing, and experimentation than the limited land airfields of the period.

A late question asks why seaplanes so often served as high-speed test aircraft despite the drag imposed by floats. Water offered far more space for experimentation than the available network of land airfields. Long open runs reduced the geographic constraint on takeoff and landing during record attempts and development work. The exchange shows how infrastructure can make an apparently less efficient aircraft configuration useful for naval-aviation research.