Simply because the source is openly available to read, the licence can still say "you can read but no touchy touchy or compiling it".

While technically it doesn't stop you from actually doing this, in a court of law you'd be found to have violated the licence. So it wrecks the idea of businesses doing it, because usually the licence holder won't care unless someone is making money from it.

Free software lets you do whatever you want, but you gotta show your code. Big difference in practice, especially when it comes to running a business.