Perhaps they do, and that is good. I found the editorial from the American Math Society at https://www.ams.org/notices/200710/tx071001279p.pdf to have been a persuasive contribution to that open discussion. (FYI, one author has spent years building SageMath.)
I'm one of the authors that spent years building SageMath; indeed, the goal of our project is to create a viable free open source alternative to Mathematica (etc.).
There's an interesting discussion of actual attempts to create open source implementations of the Wolfram Language in Wikipedia under "Implementations" (see https://en.wikipedia.org/wiki/Wolfram_Language). The first attempt was 30 years ago by Fateman and he received an official cease-and-desist from Wolfram for his attempts; he did a lot of work on open source Maxima as a result.
I think right now https://mathics.org/ is the most complete open source Wolfram Language implementation, and it uses Sympy extensively under the hood. Mathics was dead for a while when the main author got hired by Wolfram (see https://github.com/mathics/Mathics/graphs/contributors), but during the last year there has been an enormous amount of new work on Mathics.
There's an interesting discussion of actual attempts to create open source implementations of the Wolfram Language in Wikipedia under "Implementations" (see https://en.wikipedia.org/wiki/Wolfram_Language). The first attempt was 30 years ago by Fateman and he received an official cease-and-desist from Wolfram for his attempts; he did a lot of work on open source Maxima as a result.
I think right now https://mathics.org/ is the most complete open source Wolfram Language implementation, and it uses Sympy extensively under the hood. Mathics was dead for a while when the main author got hired by Wolfram (see https://github.com/mathics/Mathics/graphs/contributors), but during the last year there has been an enormous amount of new work on Mathics.