To me, his massive amounts of scheming, plotting, diplomacy, and political dealmaking are more of a lawful bent (deals aren't deals if you don't follow through on occasion.) Thus, he is the most Neutral Evil-leaning of the demon lords because that one huge aspect to him brings his placement on the Law/Chaos line more towards the middle.
Now if anyone wants to quibble about how far towards the middle he falls (and if he actually moves out of "chaotic evil"), I'm not going to argue with you. But comparatively, Graz'zt to me is further left towards neutral evil than most of the other demon lords.
And the only reason I brought it up in the first place was because it was pointed out that many archfey (which I had placed in my "chaotic good" quadrant) weren't actually that good (more towards CN or even some CE in the case probably for fey like Maab or the Prince of Frost.) Which, sure... I get that. But by the same token that not every single archfey falls within the predominant alignment category of "chaotic good"... I don't see every single archdevil being equal in "lawful evilness" and every demon lord equalin "chaotic evilness". And likewise... not every single Angel will necessarily be the paragon of "lawful goodness" either. And we already know this because of how Zariel was portrayed having moved from Lawful Good to more Lawful Neutral when she went to the first plane of the Nine Hells to spy (before she went full LE).
Quite frankly I myself don't have much need or desire to fill out all nine "squares" on the alignment grid for entity exemplars because the Neutrals are just wishy-washy enough that it isn't as interesting to me to do so. So if I only care about the four corners... the four most devoted alignments... I'll just taken our Big Four entity sets (devils, demons, angels, fey) and find places for them. And all the minor league groups (Modrons, Yugoloths, Slaad etc.) can probably find spaces in the grid if anyone cares, but I'm personally just not going to focus on them. YMMV.