Survivor bias, there are less Islamic fighters now than any point in the last two decades
Factually incorrect, because you mentioned two decades, let's put the year 2004. In 2004, the arena of religiously motivated struggle and people who fought for religious motives are the Taliban in Afghanistan, Al-Qaeda networks most notably in Sudan and Pakistan representing the Sunnis, and Hezbollah representing the Shia in Lebanon.
2024, the Taliban is now back in power in Afghanistan, they have a similarly inspired TTP in Pakistan. Al-Qaeda networks have somewhat "localized" and even gave birth to new multitude of Jihadi group, ISIS used to be called Al-Qaeda in Iraq before transforming into a separate militant group that spans continents, and some of its proxies eventually become its own major (rival) jihadi group like HTS (used to be called JaN >> JFS >> HTS).
Just like most Al-Qaeda networks, many of their fighters eventually switch sides or create rival jihadi groups that are loyal to the Islamic State, such as the case of JNIM and IS-Sahel, or Boko Haram and ISWAP de facto creating an even larger agglomeration of Jihadi groups that competes and attracts more people fighting for what they believe is a religious cause.
in 2004, the Houthis were considered a minor armed group that was not on anyone's radar, hiding behind mountains. In 2024 they're playing the big dick game by closing the Mandeb Strait.
The PMF in Iraq was not really a hit as well, until very recently (2014) and those PMF are religiously motivated.
In 2004, for example, Southeast Asia only had Jemaah Islamiyah which was considered a threat, now there are two with the addition of IS-SEA and its many sub-groups in the Philippines and Indonesia.
In 2004 there is no Jihadist war in Mozambique, in 2024 you have the insurgency in Cabo Delgado, led by the local chapter of the Islamic State.
I'll leave it for people to debate which struggle is legitimate (Sunni v Shia, Salafists v Deobandis, Islamic nationalists v Islamic internationalists (Caliphate)) but the trend in the Middle East right now is more and more people are encouraged and encouraging themselves to join the struggle mainly due to religious motivation. And that religious motivation is none other than Islam. The attacks against Al-Aqsa and the situation in Gaza only serve to double or even triple the projected number of people who will join the Middle East power struggle game in the name of religion and more specifically in the name of Islam.
The fact that people in Palestine choose to celebrate the more Islamist-leaning Hamas than the secular-leaning Fatah is one metric to measure. This is also my observation in Syria where the secular origin struggle against Assad by the FSA eventually got swallowed by the Islamist-leaning groups where they attracted more men and talents and eventually jihadized the struggle.
With the French out of the Sahel, and the Americans getting squeezed inside their camps in Iraq and Syria, there's every reason to believe that the trend of religiously motivated movements will grow, both in numbers and sophistication.