But you lose high availability, scaling to zero, and increase your CapEx. And at the end you lose money because you need 5 FTE to have them on call for every IPv4 that you self-manage (10 if it is IPv6).
And besides, it's not a fair comparison, because AWS will give you a secret cheaper price if you commit to renting at least ten thousand IP addresses for the next decade.
You can bring your own IPs to aws. The article is claiming that it is cheaper to rent them but that has nothing to do with high availability and scaling.