Paywave infrastructure is a capital cost + relatively small maintenance. The capital cost is sunk. The relatively small maintenance cost is a rounding error on large banks operating budget.
The charges for payWave are a ripoff goldmine for the providers, and there is no need for it. These charges are banned in Australia and there is no reason why they shouldn’t be banned here also.
To address a number of incorrect statements in your post - the reason Australia differs from New Zealand here is that eftpos (Payments Australia Limited) actually does charge an (admittedly quite small - $0.15 per transaction or so) interchange fee on swiped transactions, and as a result has an actual revenue model, allowing them to invest in new technology, such as creating an EMV (Chip and PIN) application to install on multi-network cards. When you get an eftpos (not scheme debit) card in Australia, it supports contactless because it has the eftpos "CHQ/SAV" application loaded onto the chip, and can communicate with contactless readers. This means an eftpos card can be tapped for a negligible $0.15-$0.30 transaction fee.
EFTPOS (New Zealand Limited) and Paymark do not have an EMV application that can be loaded onto a chip/NFC card to communicate with contactless readers. As a result, anytime a card is tapped, it must traverse scheme debit rails. This wouldn't be so bad since contactless payments via scheme rails are actually heavily discounted compared to inserted except for the next two issues.
Blended transactions. In both Australia and New Zealand, banks push blended rates where all credit and debit transactions are charged at a flat percentage rate. In New Zealand, banks are required by the Commerce Commission to also offer what's called Interchange Plus - this is where transaction fees for any transaction are the published interchange rates from the scheme network plus a profit margin specified in the merchant agreement. The issue there is that an interchange rate for a tapped Mastercard in New Zealand could be 0.50% (for a credit transaction), or it could be 0.40% (for a debit transaction), or who even knows what it would be if it's a foreign card. And if that same card is inserted, it could be 0.90% (standard credit), 0.50% (standard debit), 2.05% (elite credit), or 1.30% (premium debit). Due to this complete mystery of charges, most merchants say screw it and choose to pay a blended rate of 1.5% or whatever for all cards except inserted or swiped cards with CHQ or SAV selected.
In Australia, there is no requirement to offer interchange plus pricing, so banks only offer blended rates of usually around 1.5% to anyone without enough size to force the bank to offer a custom agreement. Unlike New Zealand, banks include eftpos (CHQ and SAV) in these blended rates, meaning that the bank charges 1.5% on a transaction where the issuer only receives $0.15. Square and PayPal at 1.75%+ are even more usurious. As a result of this, though, in Australia no merchant only accepts eftpos, but credit is also accepted whereas NZ quite often is "EFTPOS only". If the merchant in NZ chose interchange plus, they would actually be better off getting all credit card users to tap and forbidding inserting the card!
Multi-network cards. In Australia, since contactless cards can also present the eftpos CHQ/SAV application, it is possible for the acquiring network to perform something called "Least Cost Routing". This is where when a card is tapped, the terminal determines if it is a debit, credit or eftpos card, and if the card is a debit card whether the transaction can be halted and redirected off scheme rails and onto eftpos rails. This obviously only applies where the acquirer fee is not blended, and most acquirers also block LCR from being enabled if automatic surcharging is enabled. This is even possible with Apple Pay.
Interchange also funds another key part of the system as well - fraud protection. For an in-person transaction which it is determined was not authorised by the cardholder which was tapped or inserted, the cardholder is not liable for that cost and neither is the merchant. The cost of in-person card fraud is borne by the banks, and spread across every transaction, everywhere. This is part of why noone in the world has regulated interchange down to zero. It also covers the cost of ongoing research and development for things such as tokenization (the underlying technology behind Google Pay and Apple Pay).
And to the last incorrect statement - there is absolutely no additional charge for using Contactless. And even if there were, Australia has absolutely not banned it (so stop talking about it before CommBank hears and implements one). As stated above, contactless is actually cheaper for the merchant if they aren't on blended rates. The (totally wrong) perception that there is some sort of "paywave fee" is because if the card was inserted in NZ and the customer chose CHQ or SAV, it would have cost them nothing over EFTPOS rails, but because they tapped and NZ has no contactless EFTPOS or LCR, it was sent over the (probably blended, because merchants never choose interchange+) scheme rails.