Why use unnecessary words when the verbs 'is' and 'has' have the same subject? In addition, using 'there is' puts the focus on 'a wide area of grass'. Presumably the writer wants the focus to be on 'the large swimming pool' - that's why they have used it as the subject both times.

The writer has gone to great pains to explain that the campsite has its own surfing school. So it looks like it is just a continuation of the writing style that the writer began writing in. You will notice the writer consistently uses the has structure for every detail that the writer explains. Apart from the opening sentence where the writer specifically points out the campsite's ownership the surfing school. From thereon in you can use either "has" or "there is". You are correct you can use either for where it is underlined in red.

You can do it either way. However, the sentence is simpler with "has" because that way it has just one subject ("pool"). If you said "there is a wide area of grass around it", you would create an independent clause capable of standing alone as a complete sentence. If you choose to do that, you might as well break it into two sentences: "The pool is great. There is a wide area of grass around it."

I agree with Meg. It's just a question of style/preference. Also, THERE IS is longer than HAS, and generally saying something with fewer rather than more words is preferable.

I think it comes down to personal preference. Everyone speaks and writes a little differently. Generally, using ‘has’ as opposed to ‘there is’ makes it more possessive and uses a more active voice. English speakers tend to prefer active voice over inactive, when possible.