Torture Machines are Easier, But Torture Beasts are More Fun
Look at Hunger Games as a PERFECT example of this.
What better way to instill fear and psychological anguish in your victims than by genetically engineering beasts that look like their loved ones? Moreso, these beasts have their eyes and are out for your blood! It's kill or be killed, and the anguish you'd feel killing something you think may very well be someone you loved? ...let me go get some popcorn.
Imagine a hornet, but instead of standard poison, you get a dose of a MAJOR hallucinogenic that also has the properties of being doped up with both a powerful stimulant AND depressant at the same time. Three drugs for the price of one, and it puts you through an absolutely agonizing amount of physical torture as you try to endure its effects. Add on that the possible psychological effects because who knows what you may be seeing during that trip?
Various Cute Things Turned Deadly
Fluffy, golden squirrels who like to be in packs and thrive off the taste of human flesh, butterflies that think they're bees, and cotton-candy woodpeckers with an interest in the worm inside your skull that is your brain... These all exist to be reversals of expectations in that you think they're safe because they're cute and you've seen similar that were harmless, so surely these are harmless too... Right? It's the same reason why children, animatronics, and other seemingly innocent things tend to make for the best conduits to deliver horror to an audience. The audience already has a reason to believe it's safe, so it's not something they're prepared for when it turns out they're wrong.
Doki Doki Literature Club Parallel To What I Was Saying...
Even if they go in knowing that it's horror and knowing not to trust the things that are innocent, if Doki Doki Literature Club taught us anything, that just makes it a challenge to lull the audience into a sense of security. (Hence why you'll hear quite a few YouTubers start playing DDLC say "Wait, did I get tricked into playing an actually normal Visual Novel with the promise of horror?!" once they've gotten through a degree of it with nothing having yet gone wrong.)
Now, this just explains the concept of "what?" but it hasn't quite gone into the "why?".
WHY would someone make these things? Because it's more fun! If you inject someone with some drugs, sure you can observe their reactions up close, but they already know to expect something from what you're putting in them. Have a wild beast that has been released into the wild (or at least a seemingly "open" area that is really a prison/punishment game) and whenever a victim comes across it (or it upon them), you can have cameras set up to watch their faces contort as they fall to the ground writhing in pain and agony as their heart starts to pulse, throb, ebb, stop, and resuscitate before going through ALL of that over and over and over again!
Seeing the look in your victims eyes as they see their loved ones turned into vicious beasts out for their blood is another precious joy no mere machine can offer. Sure, brainwashing their lover and making that love interest try to slice your desired victim works too, but that can be undone in the right conditions. Also, while there's the power of a jumpscare in that the first time, it doesn't quite meet the satisfaction as watching the sheer horror overtake someone as they see a loved one's mutilated, monstrous corpse come lunging at them hellbent on feasting on their entrails.
You want to know why the Progenitors made the Tayans? Because they saw it as a fun way to torture people who wouldn't expect nor be prepared for these torture-beasts. Sure, you could get more prolonged enjoyment from a more clinical machine... but that removes the anticipation and excitement of "when will the next show be?" By having the Tayans roaming around and some tech that they could use to observe what happens, they can get a lot more enjoyment out of each torture session because it will be at such variable points that they'll never be sure when to expect it. This creates tension and suspense for all those who view the process.
(My expertise in writing is Romance, I swear. Don't let my answer here or on the question about using blood sacrifices to make golems convince you otherwise... please.)