I think there’s a few layers to this. It’s easy to quickly say their content is vile and therefore they’re bad at radio, but that’s really only part of it. The MRW podcast regularly talks about how K&J’s content goes too far and they need to rein it in to build a new audience. What K&J do very well is the radio craft. Being engaging when telling a story, not focussing on the boring - basically all the things a CD would be teaching a newcomer. If you managing to catch a segment which isn’t vile and/or smut (which granted seems to be few and far between - I don’t listen but apparently the 7-8am hour is best for this) they are very engaging. They also know their audience well - in Sydney, they manage to dish up content that goes way to far without losing audience, because they know what they can get away with. Now that doesn’t apply to a new Melbourne audience who isn’t used to them, or the media commentator or enthusiast who isn’t a regular listener and it will be a significant negative for them in Melbourne.
Because Melbourne is full of great breakfast shows that everyone is already listening to. Kyle would make you believe that the competition is terrible, but almost every breakfast show in Melbourne is #1 quality. The typically close and stable ratings show this. So it’s not a matter of people who are waiting to move to something better. Even for people who might be intrigued and want to give K&J a go, they already have a favourite breakfast show that they’re attached to - and often in the stressful morning rush it’s easier to not change the dial and keep listening to what’s familiar. Over time people feel the need for a change - either their favourite show changes or ends), or they get bored, or their routine changes and they go looking for something new. Some people might then be willing to K&J a go. That’s typically how a lot of breakfast movement happens, and because of that, it’s almost always a slow change.