If the AT is armed on the MCP it will ALWAYS go into wake up mode regardless of FMA annunciation at the time. That is why it is called "Protection"
Not quite my understanding: (from manual) "When the pitch mode is FLCH or TOGA, or the airplane is below 400 feet above the airport on takeoff, or below 100 feet radio altitude on approach, the autothrottle will
not automatically activate."
So a deliberate design decision. If the PFCs are in "normal" mode and the AP is not inhibited you will still have envelope protection, i.e. you will get an increasing nose-down force approaching the stall, with no ability to trim it out.
As mentioned by other posters, a likely scenario is manually descending in FLCH, then reducing the ROD or attempting to level off above the selected altitude. There is no wakeup so the speed will decay; the clue is that the FDs will be commanding an ever increasing pitch down. If the FDs were switched off (as you're not going to follow them) AT wakeup would be available.
This is typical of what I call "mixed mode" flying: half automatic, half manual where neither half fully understands what's going on. All in or all out! Unfortunately, our SOPs are for AT in at all times, so we fly the example above in the sim. to demonstrate the "level change trap".