Okay, so a long, long time ago, there was this big group of people who believed in a religion called Catholicism. This religion was led by a group of powerful leaders called the Catholic Church. They had a lot of rules and beliefs that they told people to follow, but not everyone was happy about it.
Some people started to criticize the Catholic Church because they thought that the leaders were treating people unfairly. For example, some priests or leaders were telling people they had to pay money to the church to be forgiven for their sins, and some people thought that wasn't fair. Others also thought that the church was too focused on power and money, and they didn't care enough about truly helping people.
These criticisms grew over time, and some people even started to break away from the Catholic Church and create their own religions. This is called the Protestant Reformation. Even today, historians and scholars still criticize some of the things that the Catholic Church did in the past.
So, in summary, some people criticized the Catholic Church because they thought the leaders were treating people unfairly or cared too much about money and power.