When I went to my workplace I wanted to throw some rubbish away, into a dustbin in front of an apartment building. But I could not open it and wondered why. It was locked. I would have needed a real key to open it

Why the hell do the Germans lock their dustbins? In order noone else throws unauthorized rubbish into their holy dustbin? Or shouldn't it be plundered by the rapidly growing mass of poor people? Any idea? And, is there any other country where the dustbins are locked?

The situation is way worse than you discribe it.
In my town of bith there is a quarter of town where the dustbins of several neerby buildings are inside a room with massive walls and a fence with entrance on one side.
The dustbins have lightballs neerby, so you would see any thieves at night.
The fence has a giant lock and the dustbins have seperate locks themselves so the rubbish from one building can't be thrown in the dustbin of another.

If we would take the money that we spend to protect rubbish and use it for wellfare we could make this country a way better place.

If you see a very fat animal straying around your workplace, this might be the reason

But i bet this lock wouldn´t stop my cat. (mixture of persian and nordic forest cat. Big like a dog, fast as a bullet, and as strong as a tiger )

First of all she'd need a tongue like a key...

Hi, malone!

Take a look on your "yearly attendant expenses" (Nebenkostenabrechnung)- position: "garbage removal":
For one "little" (120l) garbage bin, emptied 1 time the week! On my bill, I could read: 630,00 € *ay, ay, ay, ay

So you know, why "our proper citizen" has locked the bin. It costs money - real money, when he has to order then the next larger bin! And maybe in some quarters is "waste disposal in alien garbage bins" a "popular sports art!
So, don't be so severe with your neighbours!

Yeah, I think you know, that you should use for your trash the public bins!

PS: For the original yell "ay, ay, ay, ay": please type "Los Lobos and Antonio Banderas - Cancion Del Mariachi" in youtube!

...On my bill, I could read: 630,00 € *ay, ay, ay, ay...

Exactly - in our residential complex we also have "golden" garbage containers, which are carefully closed away.

Well, of course I know the reasons. The question is, if there aren't better ways - not that inefficient, bureaucratic and bothersome - to handle rubbish and recycling.

Of course, you're right. To lock the bins is neither social nor humanlike. But I think it is in some "anonymous quarters" or metropolitan areas pure desperation to deal this way.
I'm rather happy to resident in an area that presently do not shows such customs.
And I think this is not a commonly german behaviour. I have seen this also in France.