If you didn't stop posting you may had enough activity and merit to rank up already. If you use forum in read-only mode your activity stays same.
Some people may stop because not only activity is used again when merit started in 2018, they stop posting be ause they may be alts, because they are not having merits which helps this forum to filter away spammers and some shit posters. He may continue to post, but according to his post history, if he did not change and increase his posting quality after the implementation of merit/smerit, he can only have more activity, not merit and he will say being a full member. I will not be surprised that if there is no merit/smerit implementation, this user would be a legendary by now but on a shot posting forum, but that was changed with the implementation of merit/smerit.