Code density in APL

Its generally accepted that programmers write the same amount of lines in any language per year.
Why hadn't everyone switched to APL yet?

>>1
Reason one: Code is written once, modified ten times, and read one hundred times. So brevity of expression is nice, but not the biggest concern.

Reason two: APL's density evaporates somewhat as you move away from mathematical applications. It sucks tremendously for writing user interfaces, which is where most of the effort goes in today's programs.

PS. The financial industry already tried switching to APL. Ask them how it worked.