They’re all different professions. You may as well say, “I could go to 10 different doctors, dentists and dieticians with the same problem, and it’s likely I’ll get at least half a dozen opinions and approaches recommended”.
I’m not disputing them being a soft science but your example is bad.
I would say my example is fine...
Even within the various subsets/specialties of psychology/therapy, there's not that level of consensus you see in the hard medical sciences.
For instance, if a married couple was struggling with an issue, and went to 10 different couples therapists who all "specialized" in that type of issue (all with equivalent degrees in psychology), they'd likely get a bunch of different answers/recommendations pertaining to what the "root problem" is, and "how to address it".
There's been huge differences in "professional opinion" in that field going back to "Jung vs. Freud" (the Biggie & Tupac of psychology, if I may make a bad 90's rap reference lol)
In a field where there's a chasm as wide as "behavior is driven by how the desire for sex impacts the unconscious mind" vs. "the ego is the center of the human conscience, and it's the ego that drives awareness and behavior" (which could lead people to very different conclusions when assessing a patient), that would make it rather difficult to establish
standards of care in a professional sense.
In a nutshell, we're not talking about a field of study where credentials confer tangible expertise (like an actual medical or science degree), we're talking about a field where credentials confer "I have a subjective opinion, but I have a 6-year degree so my opinion is worth more"
As I noted before, that's why arrogance and inflated sense of self-importance (like what Peterson often displays) is fairly common among people with advanced degrees in the soft sciences and humanities, they're often the go-to for people looking to confirm their own biases.