I think what might have worked against it was the rest of the similar "placards". There's a number of them around he game, and of course lots of them in the museum, and every one of those when you read them after solving, they just give you a bit of info about the thing that you just solved. So by the time I got to that last one in the museum, and spent a while solving it to see something fairly obvious on the wall, I never even considered that looking at the placard again would provide anything beyond "It's a diving mask", and maybe some commentary.
To be honest, I didn't even think to interact with the money bag the first time after I solved that puzzle because no solved puzzle I'd interacted with up to that point, with the exception of the teleport leaf (which I hit by chance), and the chest (which was obvious) had done anything beyond just providing some flavour text (and I don't even remember if the chest needed a second interaction, or if I got the shovel immediately upon solving it now - which means if I did need to interact with it a second time, that being a game mechanic didn't actually stick in my mind)