I'll agree that it's not super common that holding onto RSUs makes sense, but I think it's more common than "rare exceptions".
Ultimately it's an investing decision. If you believe the stock price is going up at a rate faster than the rest of the market, and are willing to accept the risk that a concentrated position like that entails, then that can make financial sense.
For people who want to hold their RSUs but still want to diversify to some extent, my usual recommendation is to pick some percent of the shares that vest every quarter to sell immediately, and hold the rest. And -- critically -- to stick with that commitment every single quarter, and not fall into the trap of thinking "oh, the stock seems to be doing so well, I'll skip the sale this quarter". (Of course, a measured re-evaluation of the plan is a reasonable and good thing to do every so often.)
Ultimately it's an investing decision. If you believe the stock price is going up at a rate faster than the rest of the market, and are willing to accept the risk that a concentrated position like that entails, then that can make financial sense.
For people who want to hold their RSUs but still want to diversify to some extent, my usual recommendation is to pick some percent of the shares that vest every quarter to sell immediately, and hold the rest. And -- critically -- to stick with that commitment every single quarter, and not fall into the trap of thinking "oh, the stock seems to be doing so well, I'll skip the sale this quarter". (Of course, a measured re-evaluation of the plan is a reasonable and good thing to do every so often.)