1. As you say, to see more information about where the paper comes from.
2. It's easy to get from the abstract page to the PDF, but not vice versa.
Personally, I also think it's good for people to get into the habit of linking to a text description of data-heavy resources rather than directly to the resources. PDFs aren't that data-heavy, but there are plenty of other things that are that could do with a text landing page, and I think it's good to get in that habit.
1. As you say, to see more information about where the paper comes from.
2. It's easy to get from the abstract page to the PDF, but not vice versa.
Personally, I also think it's good for people to get into the habit of linking to a text description of data-heavy resources rather than directly to the resources. PDFs aren't that data-heavy, but there are plenty of other things that are that could do with a text landing page, and I think it's good to get in that habit.