Why do the engine lifters in a 1994 Toyota corolla have to be placed back in the same location in the cylinder head.?

Because each lifter is worn differently on each cam lobe. No lifter are cam lobe is wore the same. If you don't put the lifters back in the same spot that they were installed in when they were NEW then it will cause the cam lobes and lifters to wear out like FAST.

If you are installing new lifters on an old camshaft then it does not matter were they go. THEY MUST GO BACK IN THE SAME PLACE.