Why destroy Laketown's bridge?

[Sauron the White]

from davem

In what way, then, was he 'foiled' by the destruction of the bridge(s)? The implication is that he couldn't get to his 'enemies' as he first intended - because they were on an island in deep water.

As I have said in several places here, because JRRT does not tell us in what Smaug was foiled in, its all conjecture and speculation. What is my speculation?
Smaug could have intended to destroy the bridge himself for sheer enjoyment and was thus foiled in that plan.
Smaug could have intended to trap fleeing townspeople on the bridge and had hopes of incinerating many with one quick blast and was foiled in that plan.

And, as I have repeatedly said, if it was his intention to go on the island he had ample space on the docks which are clearly even wider than the bridge. He did not do so.

You infer that he intended to cross the bridge to justify the order to destroy the bridges. Even though that order is somewhat silly and poor military strategy against a fire breathing creature who is attacking you from the air.

Its poorly, planned out and poorly written. Burn me at the stake for that. I have no doubt that if this were LOTR, JRRT would have fully fleshed it out so that it made sense.