I've just tried testing this on mobile and desktop and can't reproduce what you seem to be reporting.
If I start a new thread and make its subject similar or identical to an existing thread, it makes the recommendation of 6 other threads. But it doesn't stop the submission of the new thread.
What exactly happens for you folk?
The reason this feature exists is because there is a cost to every new thread created. The cost is time and space. It's miniscule, individually. But in aggregate, it's quite large.
Each new thread increases the time it takes to do things like searches, software upgrades, and other operations. Each new thread also occupies just a bit more memory on the server.
If I had to guesstimate, I'd say at least a third of all threads in our database are entirely redundant. In practical terms: your forum searches could be 50% more accurate / helpful; our maintenance could be faster; etc.
It's not there to annoy you, specifically. But it is there to try to change your behavior. Which I can understand would be annoying if you're dead-set against changing your behavior. It's there to remind you that there's an alternative to creating a new thread for the same topic someone else is already discussing.