The reasons why individuals or organizations choose open source software are lower cost, security, no vendor 'lock in and better quality.
Most innovative companies no longer rely heavily on software sales, which means proprietary software has become less of a necessity. It is reported that almost all of enterprise-level companies use open source software offerings in some capacity.
Because of this shift, more critical systems are beginning to rely on open source offerings, allowing greater funding to help hunt for security bugs.
Proprietary source distributors have started to develop and contribute to the open source community due to the market share shift, doing so by the need to reinvent their models in order to remain competitive.
Many advocates argue that open source software is inherently safer because any person can view, edit, and change code. For example, a study of the Linux source code has 0.17 bugs per 1000 lines of code while proprietary software generally scores 20–30 bugs per 1000 lines.
I think Cardano should remain open source, although your idea has some merit to it.