Agreed! There must be a way to maintain the principles and benefits of open-source; the alternative, which is that all software becomes a black box, is antithetical to the same security that that choice supposedly aims to achieve.

I think companies make decisions like this from a tactics level, not realizing that by doing so they are not only alienating their customers but misunderstanding the basic (often unconscious or unspoken) social contract upon which their very existence is predicated.

Calendly already existed. Cal came along and said, ok, but what if the code were out in the open -- auditable, self-hostable. Then you wouldn't have to worry about lock-in, security, privacy, etc, in the same way. Now they are removing that entire aspect of their value prop. It may be the only thing that caused a good portion of their customers to adopt in the first place.