They don’t know you well
Some people don’t feel comfortable liking the posts of the ones they don’t know well. In such a case, those people might see your posts but never like them.
You do not like their posts
Some people only like the posts of the ones who like their posts back. In such a case, if you are not engaging with those people then they might not engage with your posts.
They don’t want you to get them wrong
Some people might assume that liking the posts of others might indicate that they are interested in them. In such a case, those people refrain from liking posts to not be misunderstood.
They don’t want people to know what they like
Some people don’t feel comfortable letting others realize what they like and what they don’t like. Those people might thus never like posts to not reveal information about themselves.
They might be lazy
According to psychologists, even clicking like requires a certain amount of effort. Some people are too lazy to keep clicking like on the posts they like.
They unfollowed you
If a person has unfollowed you on Facebook then they won’t see any of your posts. In such a case, you will not find them liking any of your posts. (See What happens when you Unfollow someone on Facebook?)
They don’t want to show that they are online
Some people don’t like posts because they don’t want others to know that they are online or that they actively use Facebook.
You post too much
If you post too much then some people might stop liking your posts as a result. Those people might still like one of your posts if it was very interesting.
They have trust issues
People with trust issues might hardly interact with the posts of others before they feel safe around them. In such a case, they might like your posts if they developed enough trust.
They are jealous
Jealousy is one of the strong reasons that can prevent a person from liking someone’s posts. Some people might be jealous of you or even jealous of the fact that you get many interactions. (See Why do people become jealous of others?)
They don’t want people to know their habits
Some people don’t want others to know their Facebook usage habits. Those people might not want others to know when they are online or how often they use Facebook.
Why People Prefer Twitter Over Facebook? Why is Twitter more popular than Facebook?