Well, the Arabs need to truly unite first. After all the Islamic Ummah was at its greatest state and was most influnetial on every front when the Arabs led/ruled/dominated the Ummah from Portugal to modern-day Pakistan (Sindh and much of Punjab).
From the Rashidun, Umayyad, Abbasid, Famitid, Al-Andalus etc.
They are the cradle of Islam after all and all the main Islamic holy sites are located in Arab lands.
Arabs don't necessarily have to led the Ummah but peace, unity and prosperity is a MUST in the heartland of Islam (Arab world) for any genuine Muslim unity to emerge.
Whether you like or dislike Arabs, it is hard to ignore this reality.
Anyway the Arabs share language, ancestry, culture, geography, Islamic and pre-Islamic history.
However different ideologies (political), different systems of governance (monarchies, republics, dictatorships), slightly different views on the importance/influence of Islam in the society, different priorities, different rivalries, make such a thing a difficult project for now.
Regional blocs (GCC), Maghreb Arab Union (once Algeria and Morocco end their stupid rivalry (from the outside at least), Libya becomes stable etc. emerging is quite realistic. I mean the GCC is in many ways very similar to the EU and US. For instance every GCC nationality can freely work and live in each GCC country if they so wish to and they have the exact same rights.
This type of system (GCC) could be copied by regional blocs in the Arab world and afterwards the non-Arab Muslim world.
Indonesia, Brunei and Malaysia could form a natural South East Asian Muslim bloc.
Indian and Bangladeshi Muslim ethnic groups are probably the closest to each other too so they could form another East South Asian/South Asian bloc.
Pakistan and Afghanistan another.
Iran + Tajikistan + Tajik part of Afghanistan another. (Farsi speaking bloc).
Turkic Central Asian states (Uzbekistan, Kazakhstan, Turkmenistan) another.
Caucasian Muslims (in Russia and South Caucasus) another.
Turkey and Azerbaijan another.
Horn of African Muslims another.
Sahel Muslim countries another.
West African Muslims another with Hausas taking the lead.
Muslim Balkan Muslims (Muslim Albanians, Kosovo Albanians + Bosniaks).
Answer is simple, there was no technological means to make intra operational, even now it would be stretch to organize such military alliance, no nuclear air carriers, subs, strategic air transportation, jet fighters and such under production of muslim populated states.
Without that you can not have essential backbone of effective and easy operable task forces even if you overcome all common disunity between countries you need to overcome this obstacle first.
And at the end also there is big problem which countries would be first among equals, lot of work, trust and connections to be interwind before such organization could take basic shape, also what is almost unsolvable issue is state governance in muslim nations, you have monarchies, republics, dictatorships etc., NATO main strenght is derived from ideological uniformity on state levels, that itself would be enormous challenge to overcome for interested countries.
Less ambitious goal could be achieved by regions and between lingvistic and cultural similar countries,
Well said.
Religion alone is not a strong instrument for nation states to align on their own.
Political commonality, shared/common interests and economic cooperation are the most important ties that bind nation states together.
Take the GCC as an example which I would claim is the only well-functioning Muslim political bloc out there.
All member states are Arab states. All are monarchies. All share a border with each other. All are societies were Islam is not only a cultural element but also plays a direct political role unlike say secular majority Muslim countries. All member states share close economic ties and have similar/share more or less the same enemy/challenges.
All this gives them reason to unite and cooperate but even then, just like in NATO and EU, there are at times differences/rivalries.
It is just human nature to be tribal. If we are not dividing each other into ethnic groups, tribes, clans, skin colour, religions, political viewpoints/ideologies, sexes, economic and social status, appearance, personality traits, nationality etc. it is something else.
The reality is also that money triumphs almost everything in today's society. Religion as a whole is also dying. Even among Muslims. You notice it online and the many stupid discussions just within Pakistan. Or the blatant racism/dislike that many Pakistanis on PDF have for each other due to peoples different ethnic groups and sects.