Why may real world data not always reflect what was learned in a clinical trial?

Why may real world data not always reflect what was learned in a clinical trial?
Which treatments are given in the hospital and which are given in a clinic?
Would drugs used to treat Alzheimer's be useful to treat myeloma or amyloidosis?
What are antibody drug conjugates?
When should a patient consider changing therapy?
What is Considered a Line of Therapy?
How can real world evidence lead to FDA label changes?
How can real world evidence lead to FDA label changes?
How can real world evidence lead to FDA label changes?