I do not believe any users are locked at trust level 3 (@sidco can verify). As far as I remember, it is based on the last 100 days.
Someone can not visit the site for a while if they were really up to date on their reading and still maintain trust level 3. Rest assured, the system works, and people will be demoted when the requirements are not met.
Also, you can vote for the new people being bumped to trust level 4 (leader/mod status). Getting more people you think would be fair and represent the forum’s morals and standards (as you would like them to be) could also help ease the feeling of unfairness and poor representation. Vote here: