Quality appears to be declining

Now I have already my second Berkeley. The first lasted long, about 4 years. I have transported working materials (books, staplers, folders) daily in him and he has not let me down. After some time, however, he had holes below - of the books corners. Waterproof he was not, that's for sure.
My second Berkeley, for about a year. He looks good, almost black with gray paw. However, the first zipper has a "target terminal point" where it remains stuck in the fabric and must be herausgefizzelt. This resulted soon after purchase. Under the same load as the previous - - Bottom of backpack is now already become very thin. He also went out of shape, did not happen so strong and fast in the previous.
The backpack is suitable as hand luggage on the plane and has a lot of volume, so you really can stow a lot of books and documents here.

But what has really annoyed me: The rain covers over the zippers can not be good pull on the zipper, fold back repeatedly. So even at the slightest bit of rain it gets wet inside. The inside pockets are coated with a water-repellent layer, which unfortunately soon dissolves by the ingress of moisture and completely water-permeable, very thin spots leaves.
If it rains more, the water comes into it - that's for sure! There is then a suitable rain protection by Jack Wolfskin - I thought in my naivety!

The other day I was in rainy weather in a store and bought the rain protection. I tried to get him over the backpack - nil. Two reseller helped - and with them the protection always only lasted as long as I do not put the backpack on his back. Once abutted the slightest train on the straps, the shell slid down again.
The seller then tried tricks that had ever devised to move to keep the shell from. Knotting, wrap the handle, all kinds of things. Nothing helped.
The last proposal was as follows: In order that the envelope holds, I should get me a clipboard and insert back, then the envelope would hold well. I had doubts, I wanted to rely on it and asked for more detail why it because there is no matching rain cover for this pack.
Statement of the Seller: For such a reasonable backpack just a rain cover is very difficult. To get a Jack Wolfskin backpack with rain protection, one must already spend twice as much. Since then was reinforced also the back.

I can not really understand, we live in a region where it can rain from time to time. Why can a brand manufacturers then produce no rain protection, can the added to buy and install?
I have the rain cover in any case be returned immediately.

The backpack is recommended, in my view
- In case of rain-free weather,
- With not so heavy content,
- Not too many hardcover books
- If one does not transport folder (who also hard corners and contribute to the fraying at).

Otherwise, I have the impression that the quality has decreased significantly.