Empty/Gross weight Vs. Max. Pilot weight

Hi All!
I'm confused by the weight restrictions on most gliders.
As an example the Lak-12 specs show the following:

Empty weight: 794lbs.
Gross weight: 1433lbs.
Payload: 693lbs.
Max. Water 416lbs.
Max. Pilot: 242lbs.(110KG)

Why is the pilot weight restricted to a max. of 242lbs? It seems to me like the
difference between the empty & gross weights could be made up of any
combination of pilot, equipment & ballast as long as the gross weight is not
exceeded & the C.G. remains within limits. What am I not understanding here?

As any of you know who have read my numerous recent questions to this group I
am a new and BIG pilot trying to figure out which ships will work for me &
learn a little more about this endeavor. I could weigh as much as 250lbs fully
equipped in the winter. That appears to exceed the limits of almost all
gliders.

Again the generous information that I've gotten from you all is just great!

Thanks!
David Roth