system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why are androids fairly common in the Alpha and Beta Quadrants during the TOS era but almost unheard of during the TNG era?

In Star Trek the Original Series Kirk and crew run into androids several times and while it's not the most common thing they run into it certainly doesn't shock or amaze them at all but then during the era of The Next Generation they say that Data and his fellow Soong-type androids are the only known androids in the Alpha and Beta Quadrants. And one time when Voyager encountered a race of androids in the Delta Quadrant they were shocked and Belona Torres even told one of them that Data was the only other android that they knew of. What was the cause of the disapearance of androids in the Star Trek galaxy between the TOS and TNG era's?
gpt
Data is unique in that he's the only android with a positronic brain, which allows him to move beyond his programming, develop as a person, and claim the title of a true artificial intelligence.

All the other "androids" are terribly, incredibly flawed.

* Automated Personnel Units - these are the droids found by *Voyager*. At first blush, they appear to have some sort of cognitive reasoning. However, it's not too long before it's discovered that they were originally built for war, and never evolved beyond their basic programming.
* Exo III - Appear in "What are little girls made of?" Might be the closest thing to a Soong-type android, but were created by an advanced ancient race that subsequently died out. Before they went extinct, the race attempted to destroy all the droids out of fear that they would do the same.
* Flint-type - Only one known android built by Flint (an immortal being that took names throughout history). It couldn't handle strong emotions, and short-circuited when it felt overwhelmed. Flint regarded it as a failure, and never tried again.
* Ilia probe - created by V'Ger to interface with carbon-based units. Really, all V'Ger did was fill a carbon-based unit with nanoprobes and take over all functions, trapping Ilia in her own body (a la the Borg). Barely a droid, and the biology won over in the end.
* Mudd's androids - created by an advanced race from the Andromeda galaxy, they were so rigid in their logic that extended "random" behavior that was unpredictable and illogical incapacitated them.
* Sargon-type - created by Sargon to host the essence of "highly-evolved" beings of pure energy, they were more avatars than functional, self-aware droids. In the end, Sargon and his ilk were unable to coexist with beings in the material realm.

There are probably more, but those are the main contenders for the title of "android." Only Data and other Soong-type models are actually successful examples of artificial intelligence in a humanoid body.