Entries in either class must be at least approved by manufacturers who must also register and pay the FIA. 8/12 hypercar teams have title manufacturer support. LMGT3 is a trophy piggybacking on hypercar. Maybe the gentlemen drivers subsidise the manufacturers and vice-versa.
What important point am I missing? I know very little about WEC but as far as I can see this championship isn't running without manufacturer involvement and support.