Hi Juliane,
I think the problem are the people that are new to steemit think they will get a lot of money for posting. In a sense, that's true too. But like everywhere in life, it's all about the content that you publish. Find something the people here are curious about. Start your own format here, be yourself and be patient. I've took a look at your profile, well... I'm sorry to say that, but there is nothing that gives me a value to upvote your posts.
You're writing that you are doing my MS at Technical University of Munich, you are working as research assistant and you plan to attend a Ph.D. program in you welcome post. Well, what is about writing about scientific or technical stuff when you are interested in it? Take a look at steemSTEM or the German de-stem. Give the community something special that they find interesting. Write valuable content about science or something technical.
If you want to separate this from your profession, then write about one of your hobbies or about your passion?
Another tip is to use the right hashtags. Here are people from all over the world, so it is not useful to write about the Berlin Beer Festival with hashtags that would be read by only about 1% of the German users here.
How about a nice visit report from the Berlin Beer Festival with a lot of nice pictures, and a readable text? Maybe also in the German language, that you reach the people that would be interested in? I think that this would be much more valuable than posting the opening hours and the adress of it.
Don't write about how to catch a girl, you can find posts like this all over the internet. And also don't call other girls stupid (Unlike other girls, German girls are well educated), it does not sound good and makes other people think that you find yourself and or the German girls better than other ones.

Yes, you can buy upvotes to get shitposts upvoted and to get around that back that you have invested. But what will be if you stop with buying upvotes? Right, your post will earn much less than the posts from people that have formed/be part of the community and write valuable content. You do not need to vilify the purchased upvotes. You could also use it for your benefit, everyone is free to decide it by itself.

I hope I was not too hard on you right now.
We can talk more about it, but then please in German :-)

Greetings