As it's stated by others also, the area was ghetto and the border to East Berlin, separated by the death strip and the wall. So "the unwanted" people located here. (they've been invited by the German government to repair the country after the young working population died in WWII)
Now the wall is gone, the place become hip again, and the people are "unwanted" again. And if you say that the local immigrants (mostly Turkish) doesn't protest, it's basically misinformation and not recognising their efforts to keep the area what it's been for many decades: a cultural hub of the misfits. (immigrants, punks, musicians, artists etc.)
https://www.bizim-kiez.de One of the main initiatives by the local immigrants. (Bizim means "our" in Turkish, and Kiez means "neighbourhood" in German)
Most of the people moved here because it was cheap and the society was welcoming the misfits. But what you say as "economic development" is destroying the culture there and pushing people out of the town. If you create a big startup hub there, all the shops will transform into hipster cafes and restaurants... Which is happening for many years and if you can't see this, open your eyes a bit. How can you expect people who live there for the last 50-60 years to pay the increasing rent, while their income doesn't because they don't work in a Startup? How can you expect a grocery store who sells cheap vegetables to compete with a vegan smoothie store, which sells the exact vegetables for 5 times the price, or even more? And after all the places will be gentrified, the rents will go even more up... then you will start protesting the smoothie prices goes up. (Which you think is happening there, which is not!)
I would argue it is mostly for the better. But of course it is not necessarily that nice for the locals who are confronted with vastly increased prices for basically anything.
The city has changed a lot and is growing and projected to continue to grow by about 50K people a year for the foreseeable future. This is good for Berlin because it definitely needs economic development as it has been living well beyond its means for some time and because it is still catching up in terms of economic activity that was lost between WW II and the fall of the wall. All this growth is increasing employment opportunities and lots investment money is being spent in this city, which is definitely benefiting local businesses.
Meeting actual Berliners born and raised in Berlin is actually not that common. Change is very much the local culture. Major changes of the 19th and 20th century originated here and were fueled by waves of people moving here. So most people you meet here are part of the problem (in terms of gentrification). So complaining about gentrification is a bit disingenuous for most.
I would say it's a shame that a bunch of anarchists get to push back economic development in what is still one of the poorer neighborhoods. They're a vocal minority and they don't speak for all. They live in Kreuzberg because it used to be a dump before the wall fell and was thus cheap. Basically, this area was heavily damaged in WW II and the West Germans put a lot of cheap housing for immigrants there (these are not the people doing the protesting). After the wall fell, it happened to be conveniently close to the former East German historical center and it became a popular place for young people moving to Berlin to settle and for poor startups to open up cheap offices.
So, most of the protesters moved there because it was cheap and now they feel entitled to live cheaply in the middle of a major world capital that is once again flourishing around them.
This city is not done growing. There is plenty of room to build and expand.