I started watching Picard last night and even though it's set after Voyager, Data and his AI are treated as unique. I've never actually watched ST:TNG, but was a huge fan of Voyager. Several episodes were dedicated to The Doctor's humanity and growth -- it certainly seemed like the EMH AI was at least on par with Data's.
So why is Data treated like a unique being? He is not the only example of an AI who grew and developed. It would be crazy to believe The Doctor wouldn't become a well known case study upon Voyager's return, especially to characters in ST:Picard who's academic focus is on AI development.
The obvious out of universe answer is that Picard the character has a much stronger connection to Data, and mixing the EMH into the plot would muddy the waters. That said, is there an in universe explanation for why no one who studies AI seems even remotely aware of the EMH (or specifically Voyager's EMH?)