Thats not true in many cases. The wholesale price cap is 7.70€ /GB. This is the price telcos have to pay other telcos for their users roaming. And this is more expensive than end-user price in the nordics/baltic region.
And now the providers have strong incentives to look for the cheapest roaming options, or if necessary band together to overcome predatory pricing. There is no reason for these wholesale prices to be that high and they will continue to be forced lower. The EU Parliament pushed for it to be 4 Euro, declining to 1 Euro over a few years, for example.