Not to sound rude, as that is not my intent, but why should they? The ex-spouse is just that: an EX. Very, very few people who divorce did so because the relationship was good; it was intended to sever the ties. While they may have mutual children, the marriage is over and thus the status as "survived by" or "proceeded in death by" is inappropriate as applied to an ex-spouse.
I mean, the children didn't keep the ties that bind in life so why should they in death?
Many of those deceased will also have a new spouse. To list an ex-spouse could be an insult.
Bottom line, it's really a matter of personal choice (if arrangements are made previously) or those surviving, but there is no room for an ex's input.
(Really, please don't take this as rude. There just seems to be no nice way to say this. lol)