The small batch multi-layer boards haven't been as affordable. Also, many of the board houses won't work with small batches for anything above 4 layers. Now this isn't an issue when you're running a full business (assuming said business is large enough to have the capital to invest in a large enough order of boards).

This is great if you're running a small prototyping lab or doing some one-off or freelance work, since it'll be much easier to get these multi-layer boards in small enough batches.