I think its just plain lazy not to pick it up. I agree that there are not enough doggy bins in the park but still pick it up and walk to the next one! Theres no excuse to leave it like some people do.

I never forget my mum when my lab was younger, This really grumpy man used to live down an alley which was also a shortcut to our house and my lab squatted down to have a pee and he shouted at my mum and tried to make her look stupid because he thought she had poo'd so my mum turned round and said not too polietly that you can sack a pee but if he has a straw handy hes free to clean it up