Donald used to be everywhere at the parks - his cartoons frequently on television and he was featured prominently in comics and on merchandise. Did audience tastes change? Not so much as the Walt Disney Company, back in the Eisner days, decided to leave him behind. His lack of presence at the park reflects how he was perceived by Eisner's branding experts - - and declining popularity was ensured through disuse of the character.
I suspect that Donald's tempestous true nature, his well-intentioned loser persona, his jealousy, anger and schemes - - are not seen as politically correct in some views as a role model for tiny children (who are now considered the sole target market for the Mickey characters).
Also, execs always seemed frustrated that he could not carry a ton of sassy or educational dialogue - - They couldn't understand him. And since true cartoon visual storytelling was biting the dust around the same time in Disney history - - in favor of heavy dialogue-oriented scripted material, the combination of factors put Donald out of business except as a recognizable nostalgic icon. He is not a key "franchise" now, just a supporting character.
The naive version on Disney Channel today bears very little resemblance to the feisty Donald that people could once relate to.
I hope the real Donald makes a comeback now that there are animators in key creative positions again. But it will take a willingness to sell him again to do it.