Why Drebbel's early submarine remained a curiosity

How did other countries view the submarine demonstrated on the Thames around 1620?

They regarded it as an ingenious curiosity rather than a practical combat capability.

The Thames vessel demonstrated underwater movement under its own power. The reaction described here was interest in a technical curiosity, with little confidence in its use for combat. A successful demonstration did not establish a practical naval capability. No individual foreign government's response is identified in the brief answer.