Q. Can someone explain me why everything is impermanent?
Anywhere in Thripitakaya, does it say everything is impermanent because of Karma?

A / R. Simply, it’s because, the causes and conditions for the arising are impermanent, not JUST because of Kamma.
In other words, conditioned things are getting impermanent and nonconditioned thing(s) is(are) not getting impermanent.
Except Nibbana, everything else is conditioned.
Note: The Nibbana cannot be called a thing, place nor any other words. We use words just to mention It, otherwise It is “beyond explanation”.

“Bhikkhus, form is impermanent. The cause and condition for the arising of form is also impermanent. As form has originated from what is impermanent, how could it be permanent?

“Feeling is impermanent…. Perception is impermanent…. Volitional formations are impermanent…. Consciousness is impermanent. The cause and condition for the arising of consciousness is also impermanent. As consciousness has originated from what is impermanent, how could it be permanent?"

(https://suttacentral.net/en/sn22.18
http://pitaka.lk/231033/cs,aps)