There is a limit to the number of days a host can rent their space in Amsterdam to 60 days which is why you are finding a very low availability. The best hosts will have exhausted their amount by the time summer rolls around. http://fortune.com/2016/12/01/airbnb-rental-limits-amsterdam-london/.
https://www.airbnb.com/help/article/1624/i-rent-out-my-home-in-amsterdam--what-short-term-rental-law...
As a host yourself, you have probably heard guests complain about how many requests they need to go through to get a reservation. Not all hosts are as vigilent as they need to be about their calendars or their settings. Going through this the way you are is what gives Airbnb a bad name - unattentive hosts who decline because they aren't paying attention to their listing. I would recommend a host with Instant Book turned on and the Superhost logo, then look at how long they've been listed on the Airbnb (#of reviews and the dates of those reviews plus on the host profile when they joined Airbnb). Someone with some time under their belt will be more knowledgable and likely to upkeep their listing information appropriately. Of course, this is not a fail safe.
As a fellow host, you get reminders from Airbnb all the time to help keep you current on your reservation requests and calendar. When these hosts decline, they will be prompted to update their calendars. You can lead a horse to water but you can't make them drink, I'm afraid.
Good luck and have a great vacation.