Games companies have a long history of being viciously litigious to emulator developers, one that still hasn't entirely faded (witness the number of ROM and abandonware sites that still studiously avoid anything Nintendo or ESA).
Non-commercial use clauses were and are common with emulation software because the perception is that this crosses a potential line into which such litigation becomes clearly justified, and there's legal history to back it up. Both Bleem and Connectix were essentially sued into oblivion for attempting to sell commercial console emulators.
It's also something of an ethical line in the sand. Copying or cloning old games that no one is making money on anymore for personal use is a gray area as it is, but crossing the line into trying to charge money for it was seen as exactly the sort of piracy people associate with shady companies in Hong Kong and bootleggers selling bad CD-ROMs at county fairs.
So it became pretty much standard practice for a lot of emulators and emulation sites to have explicit non-commercial use clauses in their TOS or licenses.
Non-commercial use clauses were and are common with emulation software because the perception is that this crosses a potential line into which such litigation becomes clearly justified, and there's legal history to back it up. Both Bleem and Connectix were essentially sued into oblivion for attempting to sell commercial console emulators.
It's also something of an ethical line in the sand. Copying or cloning old games that no one is making money on anymore for personal use is a gray area as it is, but crossing the line into trying to charge money for it was seen as exactly the sort of piracy people associate with shady companies in Hong Kong and bootleggers selling bad CD-ROMs at county fairs.
So it became pretty much standard practice for a lot of emulators and emulation sites to have explicit non-commercial use clauses in their TOS or licenses.