Because it can be dangerous if misused.

It's a steroid, so body builders would use it constantly. It's a sex hormone, so people would use it to masculinize themselves and amp up their sex drive, and it's part of the pubertal cycle so children exposed to it pre-puberty can have masculinizing pubertal side effects before their actual puberty starts.

All steroids have a very high risk of misuse, it's incredibly easy to get your body addicted one way or another and it's one of those things that's very hard to fix after the fact.

Taking extra testosterone can be acutely rewarding and stimulating. It has moderate addiction potential.

It also creates physical dependence by suppressing your body’s production, resulting in testicular atrophy. Some people who experiment with testosterone discover that it can take months or years to rebound, if they can at all.

My main point of skepticism about repurposing is whether this is giving any of new and actionable information. It seems to be reliant on pre existing target annotations, and qualified targets already have molecules designed for them. Is the off-target effect strong enough to give you a superior molecule? Why not just start by picking a qualified target and committing to designing a better molecule without doing all the off target assay stuff first?

I side with you. The more you know, the more you discover what you don’t know.

Every attempt to consider the extremely complex dynamics of human biology as a pure state machine, like with Pascal, deterministic of your know all the factors, is simplification and can safely be rejected as hypotheses.

Hormons, age, sex, weight, food, aging, sun, environmental, epigenetic changes, body composition, activity level, infections, medication all play a role, even galenic.