Posters have mentioned the lateness of Easter, but what they aren't mentioning are the more expensive prices. We are also in a time of (inter)national uncertainty, especially concerning travel to the USA from outside the USA.
Some years ago, Easter pricing wasn't all that bad, and before FP+, if you got up early, you could still manage to ride almost everything.
Folks tend to go once a year or less to WDW, so they've tried FP+, and gave WDW time to work on the details.
I'm not trying to debate FP+, but many casual visitors now think FP+= only 3 FP, and tiered at that.
Hotel/airfare prices for peak weeks like Easter have gone up and up, while the amount of e-rides one can enjoy with a FP (relative to FP-) has gone down.
Also, in one sense, April isn't the ideal time to go to FL, it is a little too late in the spring. North Americans who live in a place with cold winters visit FL to escape snow/cold/darkness, but if you go to FL in mid-April, you miss part of spring.
Put all of the above together, and they could contribute to lower bookings Easter week. Though that isn't to say there won't be any last minute deals or folks to take advantage of them.