Another important reason why it may (and, honestly, probably) is more severe: much of BP is per se about signs rather than symptoms, really. It's about how others see you, while you might not, probably don't fully or at all, recognise it.

I needed people to tell me I was basically, crazy. I had no idea that I was in any way before that time.

I thought it was dyslexia together with anxiety. Others really saw me as crazy and somewhat dangerous maybe, even. I kept believing it must've been what I would admit maybe being, an anxiety disorder.

It took months of enduring mania and mixed states and manically goal-directed (scientific) research to find out for myself that it was BP.

Even though I was extremely manic for a very long time, I still thought it was probably subsyndromal, not severe enough to warrant treatment.

That experience convinced me it really was BP. I was rather chronically delusional for most of my life, but only very gradually I came to recognise that it was very much off. I did know there was something going horribly wrong, but I didn't recognise it as severe depression for years with lots of incapacitating, disabling, confining delusions and some hallucinations (I have quite a lot of disorganisation and delusions, but not very obvious hallucinations and not very often, or frankly I don't care much or fear them much, sometimes only recognise them as such (years) afterwards, but they did have an influence, pretty much completely below the radar).

It's basically disorganised SZ with a means of escape in BP. I had no idea whatsoever most of my life. I just couldn't or didn't do stuff. I had a vague idea others had it a lot easier, but that's it. I didn't know to what extent that was true.