Like, suppose I want to send a physical letter to my bank. I can either ensure it can't be opened (using TLS), or I can get a trusted mailman to bring it to the mail central (using a VPN or trused ISP), but only one of those measures are going to protect me against a malicious mailman carrying it from the mail central to the bank.
Because banks famously love spending time and money on IT security... Anyway, if TLS was broken, that would be a big problem for everybody.
Using a VPN to protect against a zero-day in TLS, is sort of like hoarding gold to prepare for a collapse of society, in that it's a very unlikely scenario, and if it actually were to happen you'd have a bunch of other problems that aren't solved by gold / a VPN.