Also can I use kevita to make SCOBY

Why can't I do this?

Let's say that I know that I want to make all lavender kombucha.

Why can't I use a lavender kombucha to make my first SCOBY.

Everyone says that it'll mess up the SCOBY but no one says why?

Also everyone says that I need to throw away the starter tea that I used to make the kombucha.

Why?

I plan to make a huge amount of starter tea and drink it while the SCOBY is growing