When you think of the hundreds of cartridges we have out there a lot of them would not be necessary in an "ideal efficient" world. Once you had one that did the job then why build another.
From what I have heard the 240 Apex can more or less replicate the 243W so why did the 243 get developed. Just the marketing power of a company like Winchester I suppose.
From another perspective it would be boring if we only had the 50 ( my guess) cartridges that we needed.
Rick