Energy and matter are neither created nor destroyed.
Consequently, the building blocks of existence are actually finite parts.
To create things in "tomorrow" which are new, something has to be dismantled to leave spare parts for tomorrow's new thing.
The old thing deteriorates, (dies/disintegrates) and the parts become available to make the new thing.
Time travel requires going to a place where TODAY'S parts are available to be rearranged.
Some of today's things persist as they are, of course. They only travel through time by persisting as they are. (Mountains, for example.)
Try a thought experiment. (Remember, energy and matter can neither be created nor destroyed....only changed). Imagine the total content of all energy/matter as a finite box of dominoes. These dominoes are the building blocks for whatever exists. Soooooo........
You go into a room.
On the table is a box of dominoes.
You take the dominoes out of the box and build a little house.
The next day you tear down the domino house and build a domino car.
The next day you tear down the domino car and build a domino dinosaur..
At no time can the dinosaur exist along with the house or the car. Do you see why?
Each of us contains atoms that once belonged to Julius Caesar or a dinosaur or a lady bug.
Things which today ARE........which EXIST......do so at the cost of things that WERE and are no more.
Do you realize that who you were at age 12 was a different set of cells than who you are today?
You have been replaced....one domino at a time...........
Think about how you....travel......through.....time.................and your (constituency of atoms) ultimate form and destiny (parts-wise.)
What will McGyver build?