Why can't we put maschine 3 in fullscreen mode ?

You can put it into fullscreen with autohotkey, which works fine for me:

WinActivate, ahk_exe Maschine 3.exe
WinSet, Style, -0xC40000, A ; Remove title bar and borders
Offset := -20
AdjustedHeight := A_ScreenHeight - Offset
WinMove, A, , 0, %Offset%, %A_ScreenWidth%, %AdjustedHeight% ;