I’m baffled as to what makes you think that. Here’s a list of drinks and packages affected by the compulsory deposit: https://dpg-pfandsystem.de/index.php/en/compulsory-deposit-f...

Here, have a random statistic - they talk about the decrease in percentage of beverages offered in reusable packaging: https://de.statista.com/infografik/amp/8077/anteil-von-einwe... It’s apparently “only” 42% for reusables, compared to 56% for disposable ones. It’s not perfect, but It’s better than what pretty much everybody else in the world is doing.

Edit: turns out the statistica link is not so random - it’s based on data published by the federal environmental agency. More (in German) here: https://www.umweltbundesamt.de/publikationen/verbrauch-von-g...