People's usual reasons are (i) that they expect to find something that can't be found for free (and vendors' marketing materials are certainly designed to foster and reinforce that belief) and/or (ii) that they don't really expect that and are paying just for the convenience of having exactly what they need collated and put in front of them, without having to identify, judge and assess it for themselves.
There can be some truth and validity in either or both of those of those reasons, of course, but more often they lead to disappointment, and for some people in spite of the disappointment and maybe frustration, it becomes part of a behaviour-pattern, and they spend more and more in search of something rather elusive.
It's certainly a good industry for the vendors, however you look at it. Much easier (especially for them, as they typically have only a very low level of trading skill themselves) to make money that way than by trading.
The main problems, probably, are that the people who actually need the education are (more or less by definition) the worst equipped to judge in advance which products/services are actually going to help them, and that much of the information available online which purports to help them to do that is itself misleading, misguided and quite often downright deceptive, too.