Why not put crossover networks in accessible compartments?

Sorry, I was unclear about something:

Wilson, like other highly regarded makers, uses straight off the shelf parts

Here what I meant to say was "off the shelf drivers."

Hope that clarifies.

Vandersteen use a slew of high quality parts, custom drivers, graded and sorted to match within amazingly tight tolerances... and then the whole shooting match goes in the Anechoic chamber for tuning....

Treo and up filters are in a separate cabinet within the cabinet w constrained layer damping and a very unique buss bar/lug attachment to the other driver and input connection, heavy duty :-) I might post up picture on the Poverty Bay system page...

A few speakers used to come with the crossovers encased in an entirely separate box, that you then connected with multiple leads to the speaker itself.  You don't seen much of that anymore.  If I remember correctly, one reason stated was trying to avoid vibration.

Isolating the crossover from vibration is a good thing, easily accessible compartments that allow changing components is a different thing, how often a speaker need to replaces crossover parts?

I believe encase in resin helps isolating the crossover components from vibration.

Some speakers do have a separate compartment such as the Dali Epicon line. Great way to keep the parts out of  direct proximity of the bombastic cabinet. Nola and others use outboard crossovers which add wiring complexity, but totally removes the vibration sensitive parts from the cabinet.