“Can you pass me the bag of plastic blocks?”
Not
“Can you pass me the bag of Legos”
If you wanted a box of adhesive bandages. You’d say “Can you pass me the box of band-aids?” or a tissue, “Can you pass me a kleenex?”
Companies do not want their brand to become generic trademarks.
It’s not because Lego is already pural
“I have many Lego blocks”
Not
“I have many Lego”
https://en.m.wikipedia.org/wiki/Longest-lasting_light_bulbs#:~:text=The world’s longest-lasting light,off a handful of times.