Why is platform dependency dangerous for businesses?

A business built entirely on a platform it does not control sits 1 update from collapse. I have watched brands lose reach and revenue overnight to an algorithm tweak or a banned account, and I have lived it myself. Platforms are fine for discovery. They are reckless as a foundation. A feed is a rented room. A brand on a shelf is a house. Own the relationship, or rent your future from a company that owes you nothing.