I don't get it

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.

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.

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.

I've seen this happen reasonably often in audio for speakers, preamps & power amps. A certain speaker manuf was wary of users trying anything other than the hard rubber (or was it plastic?) & very sturdy feet that were factory-fitted. The whole speaker system was designed as 1 holistic component which included the feet.
I also got a very similar response from a preamp manuf - he told me that his factory-fitted feet were the best & that he had taken care of vibration control in the chassis & overall product & that adding fancy-shmancy feet would do nothing to improve the sonics.
Same deal with an amp manuf who said that using metal feet would make the sound of his amps bright & that his factory-fitted feet (very sturdy) are the best.
Quite common for the manuf to say this but as I found out, they are not always right! Experiment & listen & you might find a better feet solution for your application.

You might try what I did in my last home. Check what is under your carpet. Is it cement, plywood, linoleum? I had old hard linoleum under my carpet. I have a tall set of Dunlavy SC3's. I went and bought 6 metal cones, three per speaker. I had 2 cones on each left and right rear corner, and one cone in the middle in the front edge. The sharp point of the cone penetrated the rug and coupled directly over the hard linoleum. One last thing; you will notice that with only one cone in front, that the speaker has wobble room because there is nothing supporting the front left and right portion of the speaker base. I ended up getting small pieces of cork, about 3 inches in diameter, and gently snuggled it in each front left and right corner. That made the speaker more stable. I think that you'll find the direct coupling of the speaker/cone tip/floor a good solution. It was for me. Good luck.

Bander if you want user experience please tell us the speaker brand and model. Then with some input from others on YOUR speakers you might as your op states 'get it'.

Desingers, no matter how talented, can be of a certain mindset and nothing will sway their beliefs. Like Milpai said, try a nice sized section of tile or wood to rest the speaker when upon the carpet. It could very well be that the designer tried all manner of footings and found the best solution (doing all the homework for you).

By the way, unless you have the proper depth and know what you're doing, I wouldn't drill into the bottom of any speaker.

All the best,
Nonoise

Milpai, I'm reading anything and everything I can re various footers. I've also been reading the threads here. So yes, I am interested in user experience. The speakers did not come with anything else. I contacted the manufacturer for
any input, thinking that perhaps they've tried various products under their speakers. The 'don't use anything' response came as somewhat of a shock. I'm not asking about footers per se but rather wondering why a speaker maker would say such a thing. It makes no sense. Perhaps it will remain a mystery.

To get feedback on user experience, would you rather not check with folks who currently own these speakers you mention?
As such speakers on carpet are not stable, and I am not discussing about sonic here. They might fall at the slightest accidental bump someone gives. The least you can do is - go to Lowes/HomeDepot and get a big tile (probably $4-$8 a piece) and place them underneath the speakers. Maybe the rubber feet will make more sense then? Did you get any other type of footers with the speakers?