I don't think you can ask why some language is so and not such in a whole.
It has just evolved that way. You can find many references to the historical development of the Polish language, but they will mostly tell you only what and when changed and not why.
Sometimes, you will also be able to connect some changes to events in the history like big migrations, colonisations or even globalisation - we are now experiencing the influence of English in Polish and I am sure there is this tendency in other languages as well. For example skejter translates to skater, biznesmen to businessman and budżet to budget. As the world has become more interconnected as never before, people start using foreign words and after some time, the dictionary is accordingly adapted.
However, as you can tell more or less when some changes happened and try to expain it, I really doubt that you will be able to find out why Polish consists of numerous consonants.
Nevertheless, I wish you good luck on your linguistic trip :)