I can’t find anything, by searching online, as to what is the purpose of these joins. Maybe to make it easier to run through internally routed handlebars? So far they only seem useful in scratching my frame so I am very tempted to replace the cables.
As access to the master cylinders and hose attachment requires quite a bit of effort (i.e. unwrapping the tape), it allows for LH/RH switcheroos do be done swiftly. Not an issue on MTB’s as all master cylinders are very accessible.
If the joins are scratching your frame just get some helicopter tape and apply in appropriate locations. Most bike shops sell pre-cut kits for just this purpose.