Why did the Nazgul not succeed in Bree and on Weathertop?

[Anguirel]

I've just thought of an ingenious, flawless conspiracy theory.

We neet to examine the Nazgul at two stages-during the hunt for the Ring, and at the siege of Minas Tirith.

While searching for the Ring in the Shire, they're quite scary, but only because we're seeing them from the Hobbit point of view. They're a bit feeble and pathetic really. Gandalf can take all nine of them, Glorfindel four or five. Aragon can scare them with a fiery stick.

Nevertheless-as detailed above-despite being vulnerable shadows (ho-ho) of their former selves, at several points they could easily have grabbed the Hobbits and nabbed the Ring...so why didn't they?

Because, fair readers, if they had seized the Ring before it reached Rivendell and taken it to their master, they would be quite unnecessary to Sauron. The Dark Lord, all-powerful, would have no need to increase their power or reward them.

As it is, the Ring slipped through their fingers, they were needed to counter the threat of a possible King of Gondor with the Ring, and so they-most notably the Witch King-had vastly augmented might and command. At Minas Tirith the Nazgul are truly terrifying, riding their beasties from an older world, with dark-flamed blades, souped-up armour...

This was the state they wanted to attain. And so they let the Ring go...