During a recent flight, I was asked by an attendant during take off to remove my earplugs.
My question is: is it forbidden to wear earplugs during take off and landing? If so, why?
In the (unlikely) event of an emergency, you need to be able to hear crew instructions, which means you shouldn't use earplugs or headphones during the most critical parts of the flight, namely take-off and landing.
The fact you didn't even notice there was a safety demo is proof enough that the earplugs were detrimental to communication between the crew and you.
Of course, things are different for people who are deaf or hard of hearing, but for people who are not, it makes no sense adding difficulties in a situation where every second counts.
Not all airlines will enforce this (some will allow you to use headsets during critical phases, others not, for instance). Some may only enforce it in specific cases (e.g. if you are in an exit row). In any case, even if they don't tell you so, it's not a good idea to wear earplugs or a headset during those phases.