This shows that UPI has the potential to scale beyond India yet crypto cannot scale at all.
The fiat monetary system is itself just made up of a large number of centralized banking systems which have probably issued more units than they claim/believe. But the critical difference from private payment systems is that because the banking systems are treated as the sources of truth to represent the national currency, they can never run out of units. The way this problem will manifest itself is probably through inflation as the banks will have all these new currency units being created out of thin air due to thousands of different system flaws or exploits across thousands of different systems... These counterfeited digital units will be accepted as payment just like legitimate digital units; there will be no way to tell the difference as all the banks inherently trust each other (see correspondent banking). Essentially, fraudsters will control much of the new money minted by various centralized systems which will give them a lot of power in the markets.
The reason why crypto is important is that it's publicly auditable and cannot be counterfeited (neither accidentally nor intentionally). I believe that eventually, most economic participants will not be able to get a hold of the national fiat currency no matter how hard they work or how valuable their work is but some other people will have no difficulty getting hold of that fiat currency and they won't work at all (they won't need to). This contrast is going to be the catalyst that causes people to move to crypto as it will cause hyperinflation due to large fiat holders being unproductive members of society and crypto holders being comparatively productive.
Even MPesa has more usage than crypto has in more countries since it was launched around the same time that Bitcoin was released.
Even with all of this, cryptocurrencies such as Bitcoin having sluggish transactions per second causes those to just use centralised systems such as UPI.
Those in crypto circles keep heralding the phrase 'banking the unbanked' but it seems that those people in 'unbanked' countries have built a better system than crypto was intending to solve in under 10 years.
It stands to question crypto's relevance in the first place as a means for payments (not speculation which it is mostly used for)