Although we know that some of you want HDG mode there, we did this very intentionally. There are a few reasons:
1) If you're flying VFR, it's fairly likely that you're not taking directions from ATC (where you're really supposed to be flying mag heading). And if you airplane to go in a direction as seen on your map, say, north, you want to fly a track of 360. Flying a HDG of 360 will get you some track close to north, but it's going to vary with the wind. TRK is what most people are after most of the time.
2) People - especially non-technical people - have trouble distinguishing the difference between HDG and TRK, and also TRK and NAV (now called HSI). So, we eliminated one of them in simplified mode to, well, simplify things. Ideally, track should be called something like "direction", but, there are conventions here that we didn't want to completely turn on their head. Discovering the difference between HSI and TRK should be a little easier once there isn't a third mode.
3) If you're flying IFR, we've got the mode for you! Expert retains the discrete HDG mode, and it also adds other bell and whisles like VNAV and IAS hold.
So there you have it. It's not perfect for everyone, but that's the story, and we're sticking to it