The number of publication at IACR conferences hardly changed over the
last 15 years. At the same time, the number of submissions increased by nearly 60% while the quality of submissions stayed the same - at least according to members of the programme committees. To worsen things, the IACR community has grown and there are many more researchers active in our domain than used to be 15 years ago.
Detailed statistics on submissions and acceptance rates: http://www2.mat.dtu.dk/people/Lars.R.Knudsen/accrates.html
To better serve our community, the Board of Directors expressed its with that Conference Programme Chairs (for Eurocrypt, Crypto, and Asiacrypt) to accept substancially more papers then used to be the case and to work with their General Chair for the logistics to make this possible (using extra slots, shorter talks, and parallel sessions).