“click here” and “by this link” poor choices because the links are not descriptive. There are at least three issues I can immediately think of:
It’s an issue for all users – hyperlinks are highlighted for a good reason. They are there to get our attention, and you will often look at them out of context.
The thing is that people skim through the content of websites, so it’s not always as straightforward as assuming they will read “If you want to learn more, click here” from start to finish. They will see “click here” first, and then you will have to go back to find the context.
It’s an issue for search engines! Yes, it still is, and for the same reason – it lacks context.
As an extension of the first issue, it’s very bad for accessibility. The high-level reason is the same, a lack of context. Sometimes users will tabulate through links to find the one they need. If it says “this link” or “click here”, they don’t know what to expect.