EU was in a position where it couldn't allow a soft exit to Britain, because the whole EU would fall apart and even more behind other big economies.
(nothing)
There was no "soft Brexit" on the table. What you are asking for is the equivalent of changing the constitution of a country for the benefit of a single city. The slippery slope isn't that the country would fall apart, the slippery slope is that the country would abandon its core values for the benefit of a small group of elites that doesn't care about the country.
The stock "it's the EU's fault!" response is nonsense, again.