Oh boy, that topic has so many layers that interconnect with each other that I could talk about it all day.
Massively simplified I would say it mainly boils down that basic needs aren't fulfilled anymore. Increasing costs of groceries, rent, public transport, healthcare and taxes to name a few meet decreasing investments (monetary and political will in general) in infrastructure, social housing, healthcare, pensions etc.
People see they pay a lot but get little in return and the right-wing parties like the AfD used that to perfection by offering simple solutions against the weakest of our society for little resistance and the use of propaganda social media.
Meanwhile we fight against the powerful, the big companies, the rich and deeply encrusted structures without being able to offer simple solutions.
But don't forget, we, as in "Die Linke", had and still have a massive influx of new members, many of whom are politically active. The left is on the rise too although not as much.