Several issues.
In all only about 10% who could benefit from a Cochlear actually get it - and this % has been stable over the history of cochlear and appears worldwide.
One problem I think is basically the high cost barrier even for those with private health insurance.
Need at least silver/gold PHI
PHI also reducing due to costs of living
And then there are doctor gap fees
Public funded waiting lists usually 12 months or more after seeing the public ENT and then there are eligibility criteria.
Resistance to cochlear implants include anxiety about less of residual hearing, serious risks which are uncommon but need to be understood.
The regret rate (those who regret having a cochlear) is about 10-15%
There is also the Deaf culture and some in the deaf culture see it is a threat to Deaf Culture and sign language
While 10% of cochlear eligible patients get a cochlear, the vast majority of deaf newborns >80% in the developed world get a cochlear. I suspect this is because most early all deaf newborns are actually born to hearing parents. The problem here is that hearing parents do not know Auslan (Australian Sign Language). Deaf Australia advocates for access to Auslan from birth for deaf newborns rather than an a carte blanche automatic cochlear for deaf newborns because of evidence that show that Auslan does not result in social isolation or poor health. The argument is that the cultural barriers relating to deafness is imposed by the community and not deafness per se. They advocate for Auslan as genuine language - just a visual one rather than a spoken one - the implication is that cochlear is not necessarily needed.
