Because that is the current technological standard, which will keep growing as CPUs and GPUs become ever more powerful. Similar trends can be seen in other areas of flight sim technology, for example truly 3D cockpits, detailed and potentially world-wide terrain, "AFM" type flight models, dynamic campaigns, etc.
ED's Apache is a 80K+ poly model and flies quite well in-game. You're right, the graphics engine and API cause various distortions on the model and skin, but those with powerful enough PCs are free to max out their AA and AF settings and minimize these, as can be seen in the Apache screenshots.
The MiG-29 is being re-done as well, because it too is now behind the standards, even though it was made far later and is far better than Lock On's Su-27 model.
Working on that, too. One doesn't interfere with the other.
Besides all this, your original point was that you can't see an improvement in the new model over the old, which we found a little baffling. Considering that the new model is obviously a much more complex one, it will clearly be much more accurate and detailed.