The entry-level trial was designed to make sure that the main trials Challenger would be capable and worthy of such. The main trials weren't simple tasks that could be completed over the course of a day because one wanted to. These were trials created to find the most appropriate inheritor for the achievements of the Caventry civilization. To make the trials that difficult, a lot of precious resources were used in its development making it so that the trials couldn't be challenged casually.
In order to reduce the amount of challengers, the entry trials were introduced to the fray and their difficulty were rated A-S rank. The entry trials came in various formats but the most popular was the illusion version. By using the glass orbs, the trials could be constantly reorated and challenged without any loss of resources, unlike with the main trials.