Or you could read information posted on various areas you frequent and not look like a goof ball.
Like how ACO/FIA has disallowed race by race entries for hypercar class. Either you do a full season or you don't.
They could easily run their old car, but why take away time from their small team when it could be dedicated in one direction or another. Also ByKolles plans to build road cars along side the race car which means more work.
I haven't watched Le Mans in a long time, or the Endurance Championship for that matter, but in prior years Ferrari and Porsche were over represented. It is just very easy to convert those cars for racing.
Many areas of blame here, the biggest is any solid rules of its future. BMW is supposedly developing another GTE with the M4. Ford wanted limited glory. Aston has put all its efforts toward F1 which not only killed its LMH but GTE Pro efforts.
Though not sure where you saw four entries only, there are seven cars listed for GTE Pro. I think the four is the WEC season entry list, which was never that big. It only had 2 to 4 more cars in prior years.