Why do you think there are so few male OTs (even less than male nurses)?

I have just graduated from OT school and I am a male. Yes we are few. My class had 35-37 students and there were only 2 Males.
The class before me had 4 males and the one before that had 1.
The reason is because Ot is a new proffession- only approx 3- 4 decades old.
Many people are unaware of its existence.
Its female dominated because men generally believe physiotherapy is more better.
Ot is equally valuable to physiotherapy.
Many have a preconceived idea that the OT profession is for he ladies because that all you see. For every 30 OTs you meet 1 of them will be a male.
Not sure if your question was answered here, but I tried. The truth is no one knows.
What I would advise, is if OT attract you and you are passionate about pursuing it, then do it. The fact that you might be the only male should not matter.

How come its only 3-4 decades old? Didn't it come about at around the same time as PT?

Is being male a rather big advantage when it comes to getting accepted on a course?

Being a male does not give you an advantage, trust me. I applied to 5 universities and only got accepted by 2. Got interviews from 4.
I think the professional came to be in the 80s or 90s same a physiotherapy yes. But think about it, compared to nursing that is still very young for a profession.

Which unis did you apply to and what were your A level grades if you don't mind me asking?

The origins of physiotherapy go back a long way:

https://wellcomecollection.org/articles/XTW9ohAAACIANLbz

It is true that as a degree subject called 'Physiotherapy' that it was 1982...

Actually, OT stretches back far further than a few decades too:

https://www.rcot.co.uk/about-us/our-history

As for the male / female ratio, I think the answer is far deeper in terms of society than can be covered here. Why are certain areas such as consultant surgeons heavily male dominated? For every person you ask you will get a different reply.