- Reliability. The cloud is available with little or no downtime, to 5-8 nines (5 minutes to 1/3 of a second of downtime per year). Each nine costs roughly 10x the previous one.
- Bandwidth. Residential service may work for your own personal file transfer needs, but if you're sharing to the world, even a modest degree of traffic results in a hug-of-death.
- Security. Ideally, cloud systems are managed and monitored against network attacks, as well as affording physical security practices.
- Updates. This becomes Somebody Else's Problem.
- Ongoing development. Dittos.
It's not that these aren't addressible by individuals, but it's a lot of effort to do so, and at population levels, people are simply unlikely to be able or willing to do so. A small percentage, yes. The vast majority? No.
Raw compute power is a tiny fraction of the concerns involved in service hosting.
Smartphones are a massive leap forward in low-power/energy-efficiency, but my 2013 desktop machine (KGPE-D16) still creams every smartphone ever manufactured on any metric other than power consumption.
I'm kinda tired of hearing nontechnical people congratulate themselves on having a "supercomputer" in their pocket.