9€ or 49€ makes a huge difference.
1. For unemployed people and people in low wage jobs, 40€/month is a lot of money, and many will not be able to afford this ticket. Meaning they have to stick to single tickets, whenever it is unavoidable or use other means of transportation.
2. During the 3 month of the 9€ ticket, we saw a huge increase in travels to surrounding areas of cities. Anecdotally, there are stories of bakeries, cafes, bars at the edge of the city who saw an significant increase in customers because the barrier to visit them was lower to virtually zero. People just visited different parts of their city, or other cities because it was now affordable for them.
3. 9€ is a price where you don't think about buying anything else. The first trip you take, you buy this ticket (even on the last day of the month). This massively simplifies traveling by bus and train. 49€ is something you only spend if you know that there will be multiple trips in the month. This combined with the subscription based model, makes the current ticket far less attractive than the previous 9€ ticket.