Equating the material selection for gears in a 1500W blender vs a mechanical cat flap does not make a ton of sense. "Plastic" gears generally don't require lubrication, or can be self-lubricating or have embedded lubricants so they are often used in consumer products to avoid maintenance requirements and cost. But there also are advanced "plastics" that might roundly outperform aluminum or even steel in a gear application too. The questions isnt so much about the gear but the engineering that went into selecting it.

Unfortunately the materials choice really is often purposely manipulated to shorten lifespan, and I have direct knowledge of it happening one time. I have a friend who has his own injection molding machines and manufactures a couple of products for a popular trade brands. When he started out, he was building everything with polycarbonate. After about 2 years the brand asked him to switch to ABS because their returns under the 1 year warranty were too low. The cost difference was immaterial too; the entire decision was made to shorten the lifespan of the product. They legitimately wanted it to break out of warranty so that people would be likely to return to buy another or buy something different. Sorry don't want to name the company, but it is a respected brand.

They were right about it lasting though. I have one of the OG polycarbonate units and it's now more than 20 years old!

There's no reason they wouldn't be fine if spec'd out correctly for the conditions they'll see.