I don't get it

Thanks for the input and comments. The carpet is on an oak floor.I've decided to place 1 inch thick non resonant stone tile (perhaps granite) under the speakers and raise the speakers at all 4 corners with cones of some sort.

Here's my experience with the ESP Bodhran speakers. The speakers are supplied with spikes made of a plastic (perhaps Delrin) material with a brass pointed tip. I thought this might have been a cost saving measure to only make the tips brass. So, I ordered a set of solid brass Stillpoints.
Wow, what a difference! Unfortunately not for the better. Leading edges became way prominent and the sound lost its organic wholeness. The sound was now way Hi Fi, like a TV with the color and contrast controls set to high.
So, the manufacturers choice for the spike was well chosen based on actual listening and not a cheap out on material.
The speakers are on carpet over concrete slab.

There are many factors that have an influence on the choice of feet or spikes

One of them is the floor construction.
That varies a lot from one room to the other, and different foors need different solutions.

So it is not possible to deliver one solution for all.

But what a manufacturer could do is to provide one set of spikes and one set of isolating feet and add the information in the user manual when to use which.