Why is Search API only searching node titles?
This is probably due to a misconfiguration in your search_api view. I'm assuming you're using an exposed filter and you'll need to be sure that your Keyword Search filter is configured to also search the body field. Edit the settings for the exposed filter and make sure body is selected in the Searched fields field.

It could be helpful to configure a search_index view mode for your nodes and configure search_api to index that view mode, then you can set your exposed filter to just search on that one "field". I find that it helps to keep things running smoothly and consistently across content types that don't necessarily share fields.

Also, make sure your content is actually indexed, sometimes it's just queued and hasn't actually been indexed yet. You can do that from your index's "View" tab.