I just dont get it why they didnt mention to put transistors between it in the playground
Sadly it is not a very good example, you will note there is no resistors in although the text now tells you to do this after some badgering from a few members. The lack of resistors and overwriting of the outputs probably meant the display looked ok. There is a train of thought that goes, it is only a demonstration and people will not run it for long so overload dosn't matter.
However I think that it is important to get it right as people, like you, go on and use the circuit as a basis to expand into their own design. If you start off with the right idea you don't have to relearn old stuff.