How is it different from the cloud? Plenty startups store their code on github, run prod on aws, and keep all communications on gmail anyway. What's so different about LLMs?
Those plenty startups will also use Google, OpenAi or the built in Microsoft AI.
This is clearly for companies that need to keep the sensitive data under their control. I think they also get support with adding more training to the model to be personalized for your needs.
The main players all allow some form of zero data retention but I'm sure the more cautious CISO/CIOs flat out don't trust it.