Why do people abandon animals?

Okay now I always look on both side of a situation, even if it's a bad one,
but I can maybe understand it a little bit because some people have a reason, moving and they dont know how the "pet" is going to react, or the cost of the wellbeing (like is the dog sick or have to get surgery for a problem or even a money problem) and I their reality it's the most "normal thing" to just abandon the "pet"

but yea i agree its sick to just leave an animal behind