Yes, I do not see any source of financial gain that could motivate them for this, because both MuPDF and Ghostscript are free.

MuPDF is an excellent PDF reader, the fastest that I have ever tested. There are plenty of big PDF files where most other readers are annoyingly slow.

It is my default PDF and EPUB reader, except that in very rare cases I encounter PDF files which MuPDF cannot understand, when I use other PDF readers (e.g. Okular).