The big cost to doing it yourself is maintenance.
There is, for a lot of people, a fairly large amount of value in never having to worry about hardware dying. If it does, that’s someone else’s problem, and it will be fixed, as far as you are concerned, rapidly and without any interaction with you.
How much any given person values that is going to vary wildly, but it means that you don’t risk having stuff go down at a moment when you can’t do anything about it. Maybe you’re on vacation, and you don’t have any hands that can do anything. Maybe you’re sick, or just extremely busy that week.
You’re not wrong that this comes at a fairly substantial monetary cost, but it is wrong to say that this isn’t, in many cases, a cost that people are more than willing to pay in exchange for the benefit.
Every now and then, I try to browser without an ad blocker.
That generally lasts until I encounter something that’s bad enough that I don’t really have a choice, and then I turn it back on.
The page needs to actually function. It needs to be possible to click on something and actually be clicking on the thing that you’re intending to.
And it can not have stuff that blinks in a manner that causes a segment of the population (which includes me at times, but not 100% of the time) significant neurological problems.
That last one has been the driving force behind stuff getting reenabled a fair bit.
Oh, and if it’s ads on video content, they need to be at least vaguely reasonable in regards to interruptions and length. Youtube is way past that at this point.