when governments started subsidizing airport construction as a matter of national prestige,
the economic advantages of water landing became less important.

Without government support, (airports, regulation, standards, safety and maintenance requirements to aid consumer acceptance, navigational aids, training standards, etc), the airline industry would never have picked up as quickly as it did. By the time the jet liner came along (also at least partially dependent on defense spending) the entire ground infrastructure for the airline industry was already well in place.

This is the role government could play with space exploration.