To "fix" this, last year the government raised the cap to $35 from 1 January. And you'll never guess what has happened: prices are once again at the cap (in just nine months), so polluters will be paying it and stockpiling credits for later, compromising all future carbon budgets.
What this tells us is that the government is consistently setting its price cap too low. Even the $50 cap which will supposedly apply next year (in the form of a trigger point for the government flooding the market with credits which it does not have and blowing the carbon budget) is probably too low. If we want the ETS to actually work, we need to remove the cap, and let the market set the price. This will mean some polluters will be unable to pay the new price, while dirty farmers will face more competition from trees. But that's the fucking point. Market mechanisms work by making some behaviour - polluting - less profitable than other behaviour - not polluting. It allows clean producers to outcompete dirty ones. By artificially capping the price, the government is preventing that process from working, and thus hamstringing our climate change response. And all to protect dirty, outdated producers who could not compete if they paid the true price of their activities.
Carbon prices need to rise. Until that happens, we're never going to get anywhere. It is that simple.