I think the increased knowledge in effective carbon dosing may be one reason. I have 2 tanks set up with dosers and red sea nopox. It keeps my nitrates and phosphates minimal with very little effort. I have a refugium on another tank mostly for fun, and I am finding it more challenging that I had wanted. If you aren't running a large enough space people are also finding them not as effective, chaeto mostly needs to tumble around and the fear of some of the other macros going sexual.