The important thing to remember here is that many BOINC users are contributing much more than 5 GPUs... completely for free! They haven't joined Gridcoin yet. For example, Top SETI@home user has 98 high-end GPUs crunching for science, completely for free (actually at a huge loss, because he is literally consuming like 0.5 megawatt-hours per day).

Imagine asking the Hushcoin community to continue mining HUSH, but without payments. Their coin and their network would disappear tomorrow. But Gridcoin wouldn't.