Is it based only on your own observation or do you have any data source for this?
I suspect this is true, but I'm curious on what the actual female participation % figure is.

There could be a few reasons for that. Women are more risk averse in general, but, at the same time, are keen to participate in activities that are considered socially acceptable. So when gambling became more popular, i.e. due to mobile apps etc, more women have decided to give it a try.