This is because we aim to make as much information available as possible. Not everything that is measured in human genetics is a disease, but everything that has a significant genetic signal has an underlying relevance to target function, and hence its possible involvement in a disease.
For example, the measurement of blood glucose levels is a proxy that has information relevant to diabetes. Similarly, a cellular phenotype measured in a differential expression analysis or a CRISPR knockout assay is acting as a proxy for a function that might be related to disease.
This means that the user might find evidence that they may not have been looking for, but which makes sense to them biologically.
This post is based on an Open Targets Blog Post, where you can find further context about this decision.