Quoted

The motivation for inverting the "u" bit when forming an interface
identifier is to make it easy for system administrators to hand
configure non-global identifiers when hardware tokens are not
available. This is expected to be case for serial links, tunnel end-
points, etc. The alternative would have been for these to be of the
form 0200:0:0:1, 0200:0:0:2, etc., instead of the much simpler 1, 2,
etc.

The use of the universal/local bit in the Modified EUI-64 format
identifier is to allow development of future technology that can take
advantage of interface identifiers with global scope.