America sells British debt. Britain finds it impossible to borrow. British shipbuilding ends by 1922.
maybe the us even tells Germany that they wont take actions to enforce reparations.
You do not have a clue how bonds work do you? If you or I buy government bond we are perfectly able to sell it. We'll probably only get a discount price because it is likely some of the coupon payments have been made and besides the buyer is looking to make a profit but we can sell it. The new buyer then receives exactly the same conditions we did when we held the bond. We just have some money and no bond.
As to enforcement of the reparations payments France proved able to go about that on her own.
the treaty was designed to limit the size of warships and place restrictions on weaponry. The US threatened to build up a navy to rival the Royal Navy if UK didn't sign the treaty. But what if the UK didn't? The Great Depression would have stopped any serious shipbuilding campaigns by the US.
The Great Depression caught everyone by surprise and was not really a factor in anyone's naval calculations. Now the US Navy did have a problem of squeezed budgets and the fact that its next wave of construction in battleships and battlecruisers was going to look decidedly second rate compared to the G3s and N3s but as people have pointed out above the British had to worry about the next wave of construction after that. As people could also have mentioned the US also needed to worry about the Japanese...the Japanese also needed to take note of money worries of their own.
However the British and Americans actually had a fairly pragmatic view of what navies were for. Even the Japanese had a more sensible view of navalism than the Imperial German Navy and the German Navy League.
So the treaty basically recreated the situation that would have existed without it but on a budget. The USN and RN at the top, more or less on a level with the RN building more cruisers in practice. The IJN is able to defend Japanese interests in the Pacific but not go on a crazy conquering spree. The French able to keep the Italians in their place and so on.
We cannot be sure but I would strongly suspect that without the WNT the relative positions of the navies would be the same but all their governments would have spent a lot of money that could have been spent more sensibly.