Twitter users can limit their mentions. Twitter is currently testing a feature where mentions can be limited.
You can get access only by mentioning any user on twitter but it sometimes makes users bored.
People who are not very close to them also mention them and wear jhya. To control this, Twitter is testing a feature to limit mentions.
After this feature is officially released, it can be made unmentionable or only available to people who follow. It provides more privacy to the user.