There are many possible explanations for that phenomenon. I wouldn't necessarily assume malice.

Rate-on-delete tends to produce a lot of one star ratings, especially for free apps: if they liked the app, they wouldn't be deleting it.

For paid apps, review copies tend to produce high ratings, since getting a special freebie primes people to like the app. Developers often give copies to friends, too, and they'll be much more likely to rate than the general public.