There may be more reasons other than the ones already cited. In the early centuries, it was an era of Muslims with a zeal for knowledge of their Creator through His Creation. In more recent times, knowledge and understanding of Deen, specialist expertise in a field (academic, technical, scientific, multi skilled or otherwise), has shifted to acquisition for the self and not for the Ummah in general any more.
In the first centuries, it was in part an extension of Muslims with an excellent awareness of their Deen and a willingness to discover everything else as well, not just for the betterment of themselves personally but for society in general, the welfare of the people and an equation of disseminating what we do know with a responsibility of finding solutions to what we don't know.
When there was no danger of a person or a society's accurate knowledge of what constitutes Deen and Shariah and their individual and collective piety, other fields lied open for additional self discovery. Muslims did not envy, feel inferior to or believe in the Non Muslim civilisations. Muslims served in their own countries, lived and studied there and Non Muslims took from them. This is no longer the case.
This was for several centuries, as spoken by others before me, the age of patronisation by Muslim governments, the expansion of Islamic frontiers, a steady increase in the treasuries of Muslim empires and active encouragement for academic, scientific, technological advancement by both important political and financial sponsors.
It was not until the 16th Century when there had been a lack of Non Muslim conquests of Muslim majority lands that could seriously harm the basic structures of government, civil society, economic performance and ideological development that progress began to slow down significantly.
It was true, inventions, scientific and technological advances had started to decline some two or three centuries earlier and rulers had in larger numbers begun to indulge in investing in passions with little enriching industrial progress, but with the advent of foreign invasion by Non Muslim nations, the societies, ideals, abilities and health of the countries was severely weakened, if not partially destroyed.
We can return to that era; not necessarily of discovery itself, but of a sense of pride in our own societies, an advancement of culture and the enrichment of academic, political, industrial and cultural refinement where others can envy Islamic societies; but it is conditional, we have to return to what we were and what Allah wants from us and that is correct knowledge of our Religion, acceptance of His Creed, legislation and the purpose of Creation and that is living life for preparation for the Akhirah itself.
At present, this is little more than a dream as we are ruled by oppressive governments in Muslim countries and collectively there is more disunity and distrust than a willingness to set aside differences, so on a universal level, it is less practical, but individually we can start with ourselves and our families and go from there. If we have complete trust in Allah (and not in ourselves), we will eventually achieve victory. That is a Divine Promise.