"If you were smart, you could figure it out"
Zubat are often found wild in caves. They are massive in population,
They're commonly found in numbers in the hundreds. They're considered to be part of the ecosystem, less as a desirable or strong Pokemon and more is just a fact of the environment. They're large numbers in common pathways make them a nuisance to most people, but for some this is an advantage. For example, if you're trying to run a criminal gang and everyone in it needs a Pokemon. Zubat are incredibly easy to capture and plentiful, making them the cheapest option to give away.
When caught like this, the Zubat are not cared for. They are tools or rather weapons rather than individuals to get attached to. If one is weak, it is thrown away and replaced by another one. They are not cared for emotionally and because they are so replaceable, they're usually not taken care of physically either.
In the earliest parts of interceptions life, it was simply just a weapon. It knew nothing but fighting, attacking whatever it was told to without thinking and without any sort of will of its own. Fight attack, fight more, fly into whatever makes a bad sound.
Team rocket had taken over the Goldenrod City Radio Tower. On his own mission against them, silver managed to sneak his way in and anyone who noticed he easily defeated with his stronger Pokemon.
Friend was clearly unskilled and had never trained a Pokemon before. He yelled at his Zubat with no sense of timing, S no idea what would be effective at all clearly, and just expected the Pokemon to be able to do something. And yet, despite the complete and utter lack of directions, the Zubat had managed to use supersonic to confuse Silver's Pokemon.
Silver felt offended that a Pokemon that had such obvious natural talents was being wasted by someone who clearly had no idea what they were doing. His Pokemon still easily managed to win, but he got the electivire to pick up the grunt so silver could steal the zoo bats Pokeball.
He stole the Zubat from Team Rocket!
The next time the zoo bat woke up, it was being sprayed with potion in the lap of a human. It had never been held gently before, or had anything care for it other than just attacking. It was rather confused itself, but didn't fight or object to it.
At this point though, silver was still pretty focused on the Zubat for its abilities.