Technology and the internet are "disrupting" so many areas of the economy, and the legal profession is no exception. Clients, or prospective clients, want to know what they have to lose by just creating legal documents themselves, using LegalZoom or a similar service. It's cheaper, faster, and maybe easier. What's not to like?
Good question. The quick answer is to think of the advantages that always come from hiring a specialist to perform any service for you. Most people hire carpenters to build their house, a mechanic to fix their car, or a surgeon to remove their appendix.
There are disadvantages that apply specifically to legal documents created online. When you check the "fine print", you'll find that document prep services make you sign a waiver acknowledging that they are not your lawyer; that they have not given you any legal advice; and that they have only sold you access to software to prepare legal documents for yourself. They make no assurances that your documents are suited to your legal circumstances. You also must release them from any liability if something bad happens as a result of using their documents. (See for yourself: LegalZoom's terms of service are linked here.)
Do attorneys use standardized forms? Yes, routinely. But these forms are only used as a starting point, and to ensure the inclusion of best-practice terminology. An attorney will customize a form so that it is tailored to the needs of each client.
If you don't get your medical advice from WebMD, then you should also avoid getting your legal advice from the internet. To be sure, there's a lot of accurate and helpful information on the internet about nearly every legal issue imaginable. But only a professional can sort the good information from the bad, and can know whether the good information actually applies to your specific situation.