Legos are a magnificent piece of engineering. They really care about the product and they work within extremely rigourous tolerances. Their practical utility is underrated.
"Please always refer to our products as “LEGO bricks or toys” and not “LEGOS.” By doing so, you will be helping to protect and preserve a brand of which we are very proud, and that stands for quality the world over"
Also, though "Legos" is somewhat common in North America, it's less common in the rest of the English-speaking world.
If the company doesn't take reasonable actions to protect the mark, they lose control of it.
Ford doesn't worry about losing their brand. Lego does. So Ford regularly uses the brand as a noun itself, Lego Group asks people to not do that.
You said it yourself.
It was oddly jarring to come across Americans on the internet, who had a totally different take on this!
(yes I realise you can have "a sheep", my example isn't quite right! Perhaps it's more like sand or rice)
I've used Lego stuff on the job for prototypes and experiments as well. They're overall really good and handy, but some simple mechanical tasks can get really messy or rattly.