Why are adjunct teachers perceived as a second-class citizens by MOE?

By a former adjunt teacher (Name withheld for obvious reasons)
I am writing this letter in regards to the treatment of adjunct teachers in Singapore schools.
Adjunct teachers are considered as “support” staff in most MOE schools. They are former MOE or NIE-trained teachers who have either left the service or retired.
However, I am perturbed by how adjunct teachers are treated in MOE schools. They are seen as not permanent staff, even though some might have workloads as heavy as a beginning teacher. Some are shouldering more duties on less pay. Many took pay cuts when they became adjunct teachers.
Why are adjunct teachers perceived as a second-class citizens? Are we not teachers too? Why is MOE erasing or omitting the contributions of adjunct teachers? What kind of example are they trying to set to younger teachers?