These are not normal account signups, they are signups to become an associate member (https://join.osmfoundation.org/) which can vote in foundation elections.
The "alarm" is caused because concerted action of roughly 10% of the OSMF membership could easily tip the current wobbly balance one way or the other, and there is no guarantee that the current "hands-off, low budget approach of the OSMF would survive such an upheaval.