In The Rise of Skywalker we learn that
Snoke was cloned by Palpatine.
This shows that it's possible to clone Force-sensitive beings. We also know, thanks to the Clone Wars show, that it's possible to Force complete obedience of a clone with a bit of tinkering.
With those two pieces of information in mind, why didn't
Palpatine
create a full army of Force-sensitive beings bent to his will?
As mentioned in this answer, Snoke was simply a puppet built/controlled by Palpatine and used to foster Kylo Ren's development. When it wasn't needed anymore, it was disposed of (i.e., allowed itself to be killed by Kylo in the same manner that Sith kill their masters). Snoke's powers came from Palpatine, so Palpatine couldn't make limitless copies of the clone without spreading himself thin.
I'm guessing that it proved too difficult - the host body was too unstable. You saw how falling-apart Snoke's body was. He was powerful (we saw that when confronted by Rey and Ren in TLJ) but also extremely slow and fragile.
Just a guess though.
In the spirit of the Sith is the hunger for power. It's not unusual that the apprentices eventually kills their masters and take their places. Although this is something that they accept as part of their vision of the Force, it has to form part of a greater plan.
It would be too difficult for the Emperor to control such an army, and avoid that one of the clones decide to kill him and take his place before his vision had reached a point of no return.
The Force is not a power you have. It's not about lifting rocks. It's the energy between all things, a tension, a balance, that binds the universe together.
You can clone a Force sensitive and get a clone with a lot of midichlorians. That doesn't mean the clone will be strong in The Force.
There is some evidence that The Force itself chooses who will be powerful, such as the Virgin Birth of Anakin. If it was simply down to genetics, those clearly beneficial space wizard genes would have long ago spread throughout the galaxy and everyone would have Force powers.
Throughout Star Wars history, the Sith used to have armies of force sensitive beings (their numbers rivaling the Jedi). But they always lost, because it's the nature of the Sith to turn on each other. Multiple weaker Sith would join together to defeat their master, weakening the order. The rule of two fixes this, since now an apprentice only defeats the master if they are stronger; this preserves or strengthens the order.
This is one reason Palpatine wouldn't want many force sensitives working for him. During the Empire he did have inquisitors, but there weren't many of them and they were far weaker than him. If Vader had betrayed Palpatine and fought him with the help of the inquisitors, they would be a non-factor. Meanwhile, an army of Snokes could be a different story.
It would appear that creating a form sufficiently stable for Palpatine to inhabit was well beyond the capacity of the Sith Eternal. This lack of ability presumably includes building an army of dark side Force adepts.
The heretics of the Sith Eternal toiled, splicing genes, bolstering tissue, creating unnatural abominations in the hope that one of these strandcasts would succeed and become a worthy receptacle. The heretics would do anything, risk anything, sacrifice anything, to create a cradle for their god-consciousness.
Nothing worked. But their efforts were not entirely in vain.
One genetic strandcast lived. Thrived, even. A not-quite-identical clone. His “son.” But he was a useless, powerless failure. Palpatine could not even bear to look upon such disappointing ordinariness.
One of the central conceits of the Star Wars universe is that while cloning is possible, doing so without having the original donor around is extremely challenging. We also see (mostly in Legends stories and video games) that cloning someone with Force powers is doubly difficult.
