First of all, many big companies pay a fortune to use inferior SaaS solutions instead superior Open Source solutions; possibly because one of their CTO may have received kickbacks or promises of a lucrative job at the SaaS provider as a consequence of this deal. There are a lot of politics going on behind the scenes when it comes to procurement.
Execs at big corporations are often looking for plausible ways to spend investors' money in a way that they can capture some of it for themselves. If they choose open source or they choose cheap vibe coded solutions; there is not much money changing hands. No opportunities for insiders to covertly monetize.
And then there are a lot of security implications to using a complex vibe coded app. The AI won't be able to identify the vulnerability in any decent sized codebase unless you know what you want it to look for.