Can someone explain why the marketcap of Gulden is low compared to other coins
We are focused on actual developments, not false promises and hype, this means much slower growth but it also means that when we do grow (which is happening slowly but surely) it will be permanent and not a short lived bubble.
and why it's not on poloniex which I trade on?
I'm afraid only poloniex can explain that, as a user of poloniex - if you would like us on there - you should make it known to them that you would like them to add us.