I have missed this too. It will become more and more of an issue as new items of equipment are added to the game (a barometer, anyone?).
It could be that Rare simply did not think about this, when they introduced the speaking trumpet; or maybe it's because an Xbox controller only has so many buttons it can use. The last thing we want is another reason for Xbox players to complain how PC players have it easier.
However, I would much rather have a hot key for the speaking trumpet than the tankard - an item I never use. If, indeed, we are going to be limited to 13 hot keys (including weapons 1 and 2), then we should, at least, be able to choose which 13 items of equipment are hot.
Alternatively, allow hotkeys (on both PC and Xbox) to be "stacked". On PC, we already "I" for "Instruments"; which cycles through accordion, hurdy-gurdy and (now) drum. Similarly, for example, you could allocate "B" (for Bilge) to cycle between planks and bucket, as you frantically use both to repair and bail water; and allocate "C" to cycle between Compass and Watch ("clock").