Bing Crosby's trustees were the plaintiff in that lawsuit -- it had nothing to do with contesting the beneficiaries. A better example is Henry Ford II, whose living trust has been in and out of court for 30 years or more; or Averill Harriman, whose adult children sued their stepmother because of trust administration matters. People who don't know how contested trusts end up in probate court, haven't been to probate court. "Probate" is a dirty word after four centuries, but "contested" should be the one to avoid.
Another problem these days, at least in states when a single trust is used for all marital assets and the spouses are co-trustees, is the splitting into two trusts when the first spouse dies. The "A and B" or "survivor and decedent" trusts were meant to protect the estate-tax exemption back when it was a much lower amount. People would die, the heirs wouldn't know what the trust required, tax practitioners never looked at the documents. There are still many such trusts in existence, and some new ones seem to be written that way. Some people will sign 60 pages of anything, if you tell them everyone else is doing it. And then they won't look at it again for several decades.