We had that too until we got 4th carrier.

I decided to use the Google date limiting on searches, and found article from 2017 comparing the prices.

O2: €30 for 20GB
Orange: €30 for 15GB
Telekom: €59.99 for 12GB
4ka: €20 for unlimited data (from another 2016 article, they didn’t even have FUP at the time, only limiting for “personal use only”)

So yeah, competition did its job.