Because the things you consider work and what you consider a large burden is different for everyone.
As an example.
I exclusively run hosted apps for email and chat at this point (Outlook/Gsuite/teams/slack/etc).
I use Plex for most of my personal media consumption.
When outlook/gsuite/teams/slack/etc stop working, I realize there's nothing I can do, lots of engineers are fixing it and I move on to some other task.
When Plex stops working, it doesn't come back online until I do something.
Maybe it's just restarting it's container, maybe some update broke something and I need to downgrade, maybe the spinning bit of slowly rusting metal in my basement failed and I'm going to spend the next week fighting with mdadm because the raid rebuild goes poorly. It happens. If you're self-hosting, even if you want to claim to be perfect at deploying/running software and even if you think you can constantly upgrade things without any issue or even if you think you can leave things running on old software forever, something will eventually break. Probably software at times, definitely hardware will break.
Do you see fixing and troubleshooting these kinds of issues as a burden, or a large one? That's the question.
At this point in my life I do. If not for the cost, I'd run absolutely everything on the cloud.
The amount of free time I spend with computers is not infinite and I'd prefer to spend it doing fun new things rather than troubleshooting for the 30th time why some random ISP I was trying to send mail to is blocking my home mail server. Been there, done that, burned the t-shirt out of frustration.
Well... if you run owncloud (or any other alternative in fashion) you need off site backups and a plan for disaster recovery to match what an external service can offer. Backup machine or funds to get one at short notice.
If you use a 3rd party service they'll handle that too.