How come 'в этот момент' not ´в этот моменте'?

When ´In this situation' is translated It's ´В этой ситуации'

But why not same thing happen in ´In this moment?'

I found few more cases.

´In any case' 'В любом случае'-changed ´In any day' 'В любой день'-not changed

Can someone explain why?