Why are all the Amsterdam hotels booked for mid-April?

Pop your dates into Tripadvisor and see what comes up. Lots of hotels showed up with openings, but the B and Bs do look pretty booked - I only scrolled down one screen. If you have a few places you're specifically set on, try emailing them directly and you might get a different answer.

These two guys run an awesome B and B: http://www.boogaardsbnb.com/about-us.html. They're showing full for your dates, but if you email them, they may have a referral for you. I seem to recall they've done that in the past. They're extremely nice and honest.

Amsterdam (and all of the Netherlands) is popular in April due to the tulips. RS limited number of accommodations may very well be booked up (mostly by his readers), but there are hundreds of other places in Amsterdam that are wonderful places to stay. Just do some searches on other hotel sites - booking.com, TA, hotels.com, etc.

There have been lots of good suggestions for places to stay in Amsterdam (in all budgets) on this forum, just do a search on Amsterdam and check out some of the threads.

EDIT Try this prior thread: https://community.ricksteves.com/travel-forum/netherlands-reviews/hotel-in-amsterdam-5caaa43b-9d9e-4a16-b73f-5e52a5405a4d

Pop your dates in booking.com there will be rooms somewhere, you know, i have only been on one rs tour, but noted most of the hotels we used were not in his books, partly i iamgine so he does find them full when his tours want to use them, and partly because there are always dozens and dozens of lovely hotels and he cant put them all in his books( thank goodness) .

Using a guide book for hotels is not something i would do, thousands of folks read the books, and the books usuaully only list 5-6 hotels, bound to be a bottle neck.
Try tripadvisor and booking.com...you can book directly on hotel or use booking.com, i just check which is cheaper , , , also if booking site says its full, still contact hotel directly.

And Pat makes a good point - I don't use guidebooks for lodging either. I start with Tripadvisor for hotels and VRBO for apartments and go from there. The voluminous reviews there give me a better idea of what I'm getting.

Like the others, I never use a guidebook for choosing hotels. Give a look at booking.com (my personal favorite) and some of the other booking sites people have suggested.

I often use Rick Steves to find hotel recommendations. But you're running into several problems simultaneously:

1) You are going at a very popular time (tulips, as said above).
2) You've a bit late to try to get rooms, particularly at popular or small places.
3) Rick's books are very popular so his recommendations get filled fast.
4) Many places in Amsterdam, particularly the ones Rick favors, are converted houses that only have a small number of rooms (say, 4-20). So these will fill quickly.

So, I agree with looking at booking dot com or hotels dot com, to see what you can snag while there are still rooms available that you can afford. My experience with Amsterdam is that demand outstrips supply, so value for money is not great; be prepared to compromise on something (price, quality, location, etc) to get a room - particularly just a month before travel at this popular time.

If you find nothing to your taste and purse in Amsterdam, have a look in nearby Haarlem. A beautiful and agreeable historical city, which might come as a relief after a day in the overcrowded capital.
It's 30 mins from Schiphol airport, and some 15-20 mins from Amsterdam Centraal Station on very frequent trains.

You could see if the Eelhouse in the Jordaan neighborhood has availability. We've stayed there and loved it! Contact them directly at http://eelhouse.eu/.

Wow--thank you all so much for your help and advice! (I did try TripAdvisor, but they were only showing either very expensive or very poorly-rated hotels. I've never used booking.com and am glad to know that you all recommend it.) Because we live in Prague and can easily hop over to Amsterdam, we've decided to go another time when it will be easier to find rooms. Thanks to your advice, I will definitely book further in advance when we go! Thanks again, everyone!

In addition to April, be aware that weekends in Amsterdam are also very popular. The place I stayed in had a 4 night minimum on weekends - year-round! Most others will not have a minimum, but that does show you how much of a weekend destination the city is, mainly for people from other parts of Europe (especially the UK and Ireland).

I had this same problem for September,even booking weeks ago! No festival as I could find. Finally went the Air BnB route.