"It is" cannot always be shortened to "it's". For example:
She says freelancing is a dream job. It is, but there are several factors to consider, before taking the plunge.
Here, it would be incorrect to contract "It is" to "It's". I have a non-native English colleague who keeps making this mistake, and I would like to help her, but I'm unable to find any rules as to why "it is" shouldn't be contracted, in such cases.
I'm not even sure what to call "it is" when used this way, purely descriptively. A similar usage might be:
It's not the popular career choice people say it is.
Here again, it would be wrong to use "it's". The "It's" at the start of the sentence is fine; but definitely no "it's" at the end of the sentence. The usage seems to be when the object of the verb "is" is omitted and implied, as it refers to an object mentioned previously.
Does anyone have a more official name for this?
The top answer in the linked-to question explains that when "the object of a phrase is preposed (moved before the phrase)" its head must be stressed and must have a strong form. Strong forms, of course, can't be contracted.
However, in the example here, there is no object that has been pre-posed or "moved" to the left of the phrase. What is the exact explanation for why this verb in this example cannot be contracted?