You can always build a small search webservice that you open source and that your proprietary software calls out too, removing the need to open source everything.
Linux is GPL too, didn't hinder companies making trillions on top of it.
Linux is not a good example because of the syscall exemption. The licensing situation is not at all comparable as xapian’s original point of existence was embedding.
Linux is GPL too, didn't hinder companies making trillions on top of it.