Some of the Apple history books mention Adobe since the two companies were very close when the Mac was developed. Been a while since I read them but I Would not doubt there was support direct from Apple to try to keep them like this and money or hardware that got them to develop for Mac in the first place considering PCs were far outstripping Mac, and early Macs were hardly capable machines even for their niche market. Apple also licensed Postscript from Adobe for the main printer for the Mac in DTP, the laserwriter. This meant money to Adobe who had all their major software on Mac since it helped to sell fonts to Mac users.
Adobe made a lot on selling fonts back then. You bought Photoshop once, for instance, but you would have to buy Adobe fonts for each of your DTP stations everytime you wanted new typefaces.
Then Apple decided to go to Microsoft who had a clone of Postscript called TrueType and license that as an alternate font system for the Mac. As most clones go, the fonts were cheaper and it was already in use in Windows meaning lots of fonts and printer support was alreayd available.
So once Apple fired this 'shot' at their partner, Adobe decided to fire back. Knowing their software was what was making the Mac de-facto for DTP and graphics art they ported the golden eggs to Microsoft's platform. At this time, of course, Windows had a much larger market than Amiga and made the more logical choice as a way to slap Apple's hands and in 1992 brought Photoshop over to Windows and Illustrator in 1997. They also ignored Apples advances in the OS, refusing to use things like Quickdraw which ensured those parts of the OS would never become mainstream.
So, if Commodore (who never released a laser printer like Apple did, since DTP was not their focus for Amiga) had courted Adobe at the beginning things might have been different.
If Apple had screwed over Adobe sooner before it was clear Commodore like Mac was steadily losing ground to Microsoft things also might have been different and Adobe might have ported their software over to Amiga instead being a more capable machine, or even the ST.
So this would be a reason that makes logical sense for the lack of Adobe on Amiga
