Very briefly, most of the so called Muslims are either ignorant, misled (by Western) propaganda, or live in terrible, secular, Western-leaning/Russia-leaning dictatorships in the Middle East or Central Asia, or in mostly very poor countries of Sub-Saharan Africa and South Asia.
To some extents, one can say that Iran, Turkey (very recently), Indonesia and Malaysia are exceptions to this rule. Of these countries, only Iran has a patriotic and "Islamic" government willing to achieve greater heights in face of adversity. The remaining three countries do not want to challenge the Western powers, so they play along and can best be described as medium or upper-middle powers (if such terms can be used) in some ways.
For the Muslims to unite, Muslims must learn about each other, must change their opinions and behaviour.
Let's look at GDP since this thread is about GDP. Do Muslims operate any OIC or other Muslim organization based statistical agencies that could calculate GDP, Inflation, CPI, Unemployment, and other economic data? Most OIC statistical publications use data from Western propaganda institutes.
So called "Muslim" rulers of many so called "Muslim" countries invest multiple times more (to the tune of trillions of dinars) in infidel West rather than in their Muslim countries and elsewhere. And then there are other so called "Muslim" rulers that express their open support for the dollar when all hope for this currency was plummeting worldwide, a situation which could prove to be of devastating consequence for the West as a whole.
Many Muslims some how want to avoid responsibility by blaming all the ills on their rulers. This is not a productive way of solving problems. Rulers must be held accountable. If needed, Egyptian and Tunisian model of mass mobilization of the people should be encouraged to dethrone Western leaning regimes.
Without the people actively taking things into their own hands for their own betterment, things won't change. I have often wondered why is that every single Arab country is led by a terrible dictatorship where the government is not accountable to the people, yet the people do not reject it or voice mass displeasure. One possible explanation is that a certain (probably fake) Hadith is used by these rulers to justify their rule. Maybe some GCC members in the forum can explain it better, what excuse is used by their "kings" to justify their rule.
N.B. We know that in reality, the Quran and the Sunnah advises strongly against corruption and any other anti-Islamic practises, but these leaders not only use their paid agents to spread their message but somehow the masses have never questioned their leaders' actions, nor have they actually read the Quran and Hadiths (authentic ones) in their entirety (apparently).