All through the 18th century, European wars might end with a state losing territory, giving up claims, handing over colonies, changing its King to one the winners approved of, etc. But after the War of the Third Coalition, Emperor Francis of the Holy Roman Empire (also seperately Emperor of Austria) just... dissolved the Holy Roman Empire. All the statelets that had previously been part of it (weak as it was) were granted independence. This seems a very dramatic solution. Why did he do this?
I do apologize if an answer to this question has taken significant time, and though I had answered this to a certain extent here, I am always happy to elaborate further.
Essentially, if we follow Peter Wilson's opinion in his book Heart of Europe: A History of the Holy Roman Empire, ostensibly, imperial lawyers have phrased the abdication and the dissolution of the Holy Roman titled by Francis II as essentially releasing his imperial vassals from their feudal oaths, with the "why" being the establishment of Napoleon's Confederation of the Rhine.
To further prove this position, we must examine the actual abdication text of Francis II. This translated copy is courtesy of Wikisource:
We therefore declare by these presents that We regard the bond, which has up to now united Us to the body politic of the... [Holy Roman Empire]...., as severed; that We consider the office and honour of Supreme Head of the Empire as lapsed owing to the union of the confederate Estates of the Rhine, and that We are thereby released from all duties undertaken with regard to the German Empire and the Imperial Crown worn and the Imperial rule conducted, on its account, as resigned, as is hereby done. (brackets added)
In addition to what was mentioned above, the loss of core land of the Holy Roman Empire from the secession of the minor Rhenish princes together with the southern monarchs of Baden, Wurtemberg and Bavaria also led to Francis II's decision, if Emil Reich's assessment on the Abdication of Francis II is to be seen;
The formation of the Rhenish Confederation under Napoleon's protectorate, together with the secession from him of sixteen German Sovereigns, prevailed upon Francis [the Second] to sign the following document by which he dissolved the Holy Roman Empire.
Though it is true that Great Britain, Prussia, Russia and the other European monarchies (aside from France) did not initially recognize the dissolution of the Holy Roman Empire and up to this day is still a contention that it was made with dubious legality, the realities Austria faced after the treaty of Pressburg have made this de jure move into a de facto one.
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