Many reasons.
There is a point where closer does not help much more.
Cutting neo magnets accurately is difficult, and a Dremmel tool diamond disk does not last long at all ($20 worth of HF Dremmel-type diamond disks to half 2 original #29's lengthwise).
The dust is toxic, flammable, and explosive.
If the magnet gets too hot, it looses strength.
Breaking the factory coating leaves it exposed, and galvanic corrosion happens fairly quickly.
Thicker neos, accurately placed, should get about the same results.
Not worth the amount of cost and effort?
Can get curved magnets, or have them made.
I have at least 4 sizes of curved neos here, and did not resort to having them custom made.
G-