I'm by no means an expert, but I've been observing these brands for twenty years. My thoughts.
Most important is the watches. Many of the modern watches are not that appealing to the eyes. Lots of issues. Large cases, bad asymmetry, unnecessary text.
The case sizes are fashionable, while the mechanical complications are out of fashion. Great technical achievements get buried in dials only a mother could love.
The cases often appear to be too large for the movements, which veers my impression watches away from timeless luxury, towards fashion. This was especially apparent in Blancpain's less successful L-Evolution line.
The storytelling. Frederic Piguet was merged into Blancpain, while Nouvelle Lemania was merged into Breguet. The authentic history and regarded expertise of these movement manufacturers was suppressed, replaced with less authentic storytelling that does not sway tastemakers. Collectors who are interested in master watchmakers have the option to buy from modern day Breguets (independents), some of whom will respond to direct messages via social media. The actual history of modern Blancpain is way more appealing than the curated story.
Pricing and availability. You can get most Blancpains with a discount, but the classic Fifty Fathoms models with smaller case sizes are only available via grey market for 2x retail. Want a modern Breguet Type XX with a traditional movement and case size? I hope you were able to purchase one of the two available.
The poor performance trends of both brands could be eased by making watches that price conscious connoisseurs want to own. In my opinion, it appears that management assumes that critics wouldn't be paying customers under any circumstances, and they know the market better.