Originally Shmoneh Esreh only had 18 blessings, thus the name "Shemoneh Esreh." However, subsequently a 19th blessing was added of Velamalshinim regarding the heretics. If there are 19 blessings now, why do we not refer to it as Tisha Esreh (19 Berachot)? Why did we retain the original name of Shemoneh Esreh?
This was a question asked to me by my daughter.
I wonder if it was simply a sociological phenomena and that is why is stuck or if there was an actual idea that was being conveyed by keeping the name. As if to say it is only a temporary blessing or something along those lines.