Money is the reason why Izzys not in, so Izzys is all about money and not about GNR...
It's hard to say, as his tweet really didn't say much. It does elude to the offer (whatever it was) being for a full time gig with the band, as he can't be dumb/crazy enough to want equal pay for a guest slot.
If the offer was, in fact, for a full time gig in GNR then I have to believe he still would have made really good money. It's disappointing that his ego would hold him back from joining on this already long, long past due reunion tour. I love Izzy, but I can definitely understand why the big 3 would be getting more from this, as they are seasoned touring pros who are more iconic to the Guns N' Roses image and legacy. I know, I know, look at the song creds and all that. More to it than that I'm afraid on the business side of things.
For example, if you think that if Mick Taylor re-joined The Stones tomorrow that he'd suddenly start making as much as Jagger/Richards/Watts then I have a bridge to sell you. Same thing with Izzy rejoining Guns.
I also believe that Richard (or perhaps DJ if we're to believe what he said about Axl wanting him for this tour) was ALWAYS going to be in the lineup, Izzy or no Izzy, to "fill in" the sound. That also couldn't have sat particularly well with Izzy, as it basically shows that he couldn't exactly handle the position of rhythm guitarist on his own in 2016, after taking a quarter of a century break from from playing many of these songs live, say nothing of the Chinese Democracy songs. This would have likely solidified his position as "support" under Axl, Slash & Duff for a tour like this. Lotsa things in play here that likely turned the old grapes sour.
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