What do you mean longer than anyone assumed? We all knew it would last very long based on what we saw with the iPads.
The M1 is just an iPad chip, so we already knew.
I mean I expect M chips in Macs to follow the use effect- perceive or real- of A chips in iDevices. A are "incredible", "I can't believe it", "more powerful than anything" at launch and then "getting long in tooth", "slowing down" within only a few years, partially in support of buying the new A-series (replacement) generation. I suspect(ed) M-series to get on that very same train (in spite of common, long-term expectations that Macs should outlast mobile iDevices).
How do we collectively feel about A-series iDevices sold at the same time as M1 Macs? I'm seeing plenty of "long in tooth", "slowing down" posts implying "upgrade time." Why? Because that A series is feeling like it is no longer working fast enough... a curious effect that seems to happen every other year or three.
Conceptually, M1 devices- of which I own one myself- could be getting there by this point too. Instead, M2 is mostly M1 with some refinements, so M1 people should generally feel their Macs are just about as fast as ever, etc. I'm not seeing much "long in tooth" etc about M1 Macs yet. But I fully expect it to arrive just like it does with A-series iDevices.
I suspect if we were on the originally-imagined pace such that M3 or perhaps even M4 was "latest & greatest" right now, M1 Macs would feel like A13/14 bionic is starting to be perceived now.
Instead, I'm happy my M1 still seems fresh & robust and- if M3 Macs are still upwards of 10 months out- it may have at least that long to continue to "feel" that way before the mysterious slow downs begin to show themselves.
Maybe it won't be like that with M-series? I only have A-series as a guide influencing my imagination.