Why does VBG not allow you to drill holes into drawbeams or end plates?
This is not a stipulation from VBG. It is a requirement stipulated in Directive R55. According to the Directive, no modifications may be made to an existing, certified and registered product. Each modification, no matter how minor, requires new certification and registration. There is also a significant risk that strength would be affected, since the design is the result of extensive development work.