I've been thinking about this the last day or so and can sum up my thoughts accordingly: i strongly disagree with the decision, but it's Neil's band in much the same way another band leader like Tony Iommi, Lemmy Kilmister, Nick Cave, Billy Corgan, or Anthony Kiedis can decide to push forward with or without certain members.
Yes, I know I have cited musical examples that are mostly worlds apart from Crowded House, but they are the most fitting examples by comparison in terms of band structure. I've purposely avoided examples that are more sonically comparable examples because the ones I had in mind don't quite structurally compare.
Point being, it's his baby irrespective of how I feel.
Why do I think it happened? I don't think it's personal. Not at all.
I have a feeling it either came down to money (as it does with MANY bands), creative reasons (not sure what but...the fact Mark is being replaced with another musician allows for this possibility) or geographical logistics.
Regarding the latter; yes, I know Nick lives in Ireland but i'd say he travels out to Australia and NZ more often than Mark or Matt. I remember Neil tweeting a long while back where he wished the guys lived closer so he could work with them more often. Perhaps Neil has found a way for CH to be more of a regularity by replacing a musician who may have less qualms with long distance travel even for short stints. Perhaps he wanted someone who could answer the call on demand where Mark was unable to this time around and Neil felt this could be an issue moving forward on a more regular basis. Keeping in mind, the poster for Blues Fest have Crowded House's appearance being billed as "Exclusive Australian Performances" below their name in brackets. Maybe Mark just couldn't make the gig and Neil needed a musician but didn't want to risk Mark not being available in 2021?
Again, all speculation on my part. Either way, it's very sad news for me as Private Universe and Fingers Of Love ALWAYS sounded its best when performed with Crowded House. Yes, Mark's presence were a significant part of why these two particular tracks resonated in a live setting.