It's all so negative, that's what's wrong. What's wrong with celebrating the successes? Who cares if we finish no 15 or no 5 on the medal tally.
Ever since the heyday of recent times (yes, it's not too far away), people are accustomed to seeing Australia winning. Particularly in the pool which continues to be the major event / highlight of the Australian team, the one that attracts the most attention and the one that, all else failing, anyone would tend to remember.
The halo effect imparted from this has gone on to question the amount of funding going into sport and Olympic preparation in particular. Without "results" that the public can appreciate, people will regard the funding into sport with greater contempt and would be tempted to criticise a government who makes such investments without tangible results. The media doesn't help with this, either.
A lot of my colleagues remember the Australian contingent in this Olympics as the ones who choked under pressure, not those that gave their all etc. etc.. A lot of the people I share small talk with are already questioning the amount of funding (viz. too much) that goes into sport.
I'm not sure if more people are disappointed at the Australian team for not beating China and the US (and maybe - let alone - a crippled Russia), more than everyone was actually cut that we didn't win
more medals, especially when compared to London. That said, there's also the need to (but lack of) decide whether there was more Australians choking, or the other countries simply being the better competitor on the day (notice how there's a difference?)
tl;dr, it's business. Not the right attitude, but either an unfortunate reality or a mindset that is going to take a Herculean effort to fix.