Sealing them in potting compound reduces the impact of sound on the components. Some manufacturers also pot items to inhibit the design being copied or interfered with.
Have never seen anything like this...Paragon Jubilee, sealed crossovers?
Recently acquired a pair of Jubilee monitors with matching stands. 3/4" tweets, 6.5" mid/bass made by Dynaudio. I almost laughed the first time I picked them up...seriously heavy and inert for such a tiny speaker. They sound decent. Their construction and look alone are almost worth the price I paid for them. As a tinkerer does, I opened them up to see what's going on inside. To my surprise, the crossovers are sealed in a cylinder of some sort of resin. These were expensive speakers in their day. I assume the excellent components were used. My question is, what is the point of sealing them? I can't imagine how I'd ever update a capacitor. The resin cylinders feel permanently attached to the base of the cabinet.