Why are some puzzles rated 2600 exactly but actually rated 800-1800?

Why are they?

Such as?

If you mean that the puzzle ratings should be lower than actually displayed, it's because there are quite a proportion of players failing the puzzles even though you find the puzzles relatively easy.

Maybe you take all your time to solve puzzles, but there are always players (such as me) who blitz out puzzles and get wrong.

This one was 2600.

The diagram is not loading???

Puzzle ratings are based on pass rate. 

It has been the case for some time. Quite a lot of players, myself included, experience this.

Also, there is one particular 2715 puzzle which is supposed to be straightforward for many but a trap for those going for a king-queen fork instead of immediate checkmate.

Because chess.com has really good puzzles but a terrible system to rate them

2600 Puzzles are very common to be easy. It's a very funny happening. If they are rated precisely 2600, you know they are easy.

In fact, when I get a super easy puzzle I think to myself "This is Mr. 2600, isn't it" Then guess what? It is.