There are numerous reasons people give up, of course. Maybe they were just in it for the money, and found more lucrative work elsewhere. Or perhaps the time required was a huge barrier for them. Personal, relationship-related issues must come into some people's decision to quit blogging as well.
But I think there's one key reason not many people can be really good at it, and keep going indefinitely. And that's because it requires two opposite qualities.
Firstly, and most obviously, you have to really like writing. And you have to be disciplined enough to do it regularly. Needless to say this requires long hours sitting alone at the computer, cranking out those sentences and editing them until they express something unique, useful and shareable.
Not everyone enjoys or can even bear this kind of extended solitude. They start to go crazy if they don't have some real human contact at least a couple of times a day.
And it's social
At the same time, if you want to get your blog known, you really have to connect with other bloggers, and lots of them. There may be some people who don't actually have to do this because they are already well known for some reason. Or perhaps they write such consistently unique and brilliant content that influencers are just falling over themselves to share, link to and quote it so no networking on their part is required. But bloggers like this are very few and far between.
So, to be really successful, bloggers have to be communicative and gregarious as well as spend many hours alone working. The beauty of today's technology means that you can actually do both these things in the same location using your desktop, laptop or tablet.
You can develop and nurture these connections through blog comments, e-mail, social networks, etc. And if you need to actually talk to someone there's always Skype. So it's not really the mechanics of it that are the challenge. It's the psychological aspect. After all, they are quite different processes.
Yes, they both require a lot of communication, usually using the written word. But writing a blog article is quite different to having a conversation via e-mail. In the first case you are writing for an idealized, imaginary audience. In the second you're connecting with a living, breathing, individual human.
For this reason, individual bloggers tend to be better at one skill than the other. There are very few people who can do both well and consistently. And I think that's because each activity uses a different side of the psyche. Some people would naturally have both in equal measure, I'm sure. But I think they must be in a very small minority. Of course you can learn to develop the skill in which you're lacking. But that often doesn't come easy.
I myself prefer the writing side of things and am very happy with my own company. I do enjoy making contact with others, but I certainly don't have a huge hunger for it. And while I'm not socially incompetent, I'm not that great at socializing. As a result I haven't done enough of this, online or off, to get my blog known. That's something I've really got to address.