You still owe capital gains on the original proceeds, deferred a few years and with a possible 10-15% basis step up. This isn't zero capital gains tax.
If you happen to have a billion dollar exit on your reinvested capital gains that can be tax free, but you're still paying tax on the original gain.
If you happen to have a billion dollar exit on your reinvested capital gains that can be tax free, but you're still paying tax on the original gain.