One of the reasons why an innovation is not allowed in Islam is because, Allah sent his message to the Prophet Muhammed who was illiterate, who had no worldly knowledge, so he could not add flowers to his message to make it more understandable for us, so he would not go anymore then what Allah revealed to him . 

Another miracle of the Qur'an is, the things that are mentioned in the Qur'an 1400 years ago, such as the development of the fetus within the mother's womb, or the big bang theory, was not known to the people of that time, and these things were only recently discovered. And this was accepted by the Prophet's companions, and they preserved it, without any "buy" or "why". Because Allah knows the future, and this also proves that the Qur'an applies until the last day of this world, without any additions or improvements required, and this also proves to us that there is no need to add any innovations or improvements within the Islamic world.

The Prophet also informed us of this in his last speech:

"All those who listen to me shall pass on my words to others and those to others again; and may the last ones understand my words better than those who listen to me directly. Be my witness, O ALLAH, that I have conveyed your message to your people".

The words mentioned above tell us to keep transfering the message of Islam to the future generations of Islam, without any improvements, otherwise should of mentioned that time to keep improving this religion according to the needs of your time.

The Prophet also said in the conclusion of his last sermon:

"O People, and understand words which I convey to you. I leave behind me two things, the QURAN and my example, the SUNNAH and if you follow these you will never go astray."

This means that we cannot look here and there, to add improvements in Islam in our lives according to our requirements. We only have to focus the Qur'an and the Sunnah without any additions.

Those who claim to be Muslims, regardless how educated or how smart he may be, he or she does not have any right to add anything to the message of Allah or the examples of the Prophet , whoever tries to improve or add anything, then how can he or she claim to be Muslim. And if one does this, then there is no difference between us and the people of the Book. They are the one's who endorsed there own ideas within there books, if Moses (Musa) was a true Prophet and his book was true, then why did Jesus (Isa) come with the original Bible (Injeel)? Because innovations were done in the book of the Torah and the bible, with the excuse to understand, and trying to explain people its contents. And they wanted to make sure they made Allah and his Prophet happy, so they tried to add there own ideas, which eventually lead them to disbelief, and this is called an innovation.

Then, We sent after them, Our Messengers, and We sent 'Iesa (Jesus) ­ son of Maryam (Mary), and gave him the Injeel (Gospel). And We ordained in the hearts of those who followed him, compassion and mercy. But the Monasticism which they invented for themselves, We did not prescribe for them, but (they sought it) only to please Allâh therewith, but that they did not observe it with the right observance. So We gave those among them who believed, their (due) reward, but many of them are Fâsiqûn (rebellious, disobedient to Allâh). (57:27)

Forbidden to you (for food) are: Al-Maytatah (the dead animals - cattle-beast not slaughtered), blood, the flesh of swine, and the meat of that which has been slaughtered as a sacrifice for others than Allâh, or has been slaughtered for idols, etc., or on which Allâh's Name has not been mentioned while slaughtering, and that which has been killed by strangling, or by a violent blow, or by a headlong fall, or by the goring of horns - and that which has been (partly) eaten by a wild animal - unless you are able to slaughter it (before its death) ­ and that which is sacrificed (slaughtered) on An­Nusub^[] (stone altars). (Forbidden) also is to use arrows seeking luck or decision, (all) that is Fisqun (disobedience of Allâh and sin). This day, those who disbelieved have given up all hope of your religion, so fear them not, but fear Me. This day, I have perfected your religion for you, completed My Favour upon you, and have chosen for you Islâm as your religion. But as for him who is forced by severe hunger, with no inclination to sin (such can eat these above-mentioned meats), then surely, Allâh is Oft­Forgiving, Most Merciful.

The same thing applies, if one tries to add  there own ideas, to promote the Prophet , through his lifestyle. Then that person should ask himself does he know better then the Prophet and his companions?

Whatever action we try ourselves which is not explained through the Qur'an and hadeeth, no matter how much we consider it to be important, and we think that this action will make Allah and his Prophet happy, but instead we are earning a great sin because, we cannot cross the limits or boundaries more then the Prophet , and what he ordered us to do, and he ordered us to learn and follow the Qur'an and his footsteps, only.

For example, there is no recorded history that the birthday of the Prophet was celebrated, whether in his time, or after his death, by his companions. His companions only focused towards the Qur'an for all of there questions and solutions, and if they were unable to find it over there, then they would look at the examples of the Prophet , how he applied it. And if anyone tries to improve Islam, or adding there own ideas, which is not found in the Qur'an or the hadeeth, then this is called an innovation (bidda'a).