> Now no more results are shown in the omnibox.

I mean matches.

Rerunning autocompletion can lead to result instability in the face of asynchronous results, e.g. search suggestions.  It requires some seriously crazy plumbing to try to preserve the existing selection even across potentially losing and then regaining the selected item.  We used to do something like this many years ago, and it turned out that things were simpler, less buggy, and often less strange to use when we did not rerun autocompletion.

The case of trying to delete tons of items from the omnibox dropdown is extremely rare; most people use the history page to do this sort of thing.  So the cost/benefit here doesn't make sense.