Please help! Exterior Sliding Door Leak on Interior Slab - No visible threshold - 1980 construction
Often contractors will use styrofoam as a “blockout” for something to be installed later and they are not sure of the exact size of it. 

That is to say, the contractor could have installed the styrofoam 10” wide so the sliding door frame and threshold could be installed 1/4” below the top of the finish floor slab. (They even sloped it so any infiltration from moisture would drain outside.)

If the threshold is installed 1/4” below the finish floor level, then when it leaks under the threshold, water won’t run into the room. It will be stopped by the lip of the concrete slab. (Unfortunately the recess extends too far into the room.)

To me, it looks like the sliding door is damaged (missing part of a threshold) and the entire unit needs to be replaced. When you replace it, you can set it in a bed of sealant and a flashing “pan” to keep it from leaking.