1. Changing your domain name isn't easy. You can easily lose PageRank, email addresses stop working, OAuth has to be reconfigured, it may lead to downtime, etc.
2. The .eu domain is practically deserted. Nobody cares about it. There's no real benefit to freeing up names in this TLD.
Together, we see that this is a classic EU move - interpret the rules in whatever way is most spiteful towards anyone who doesn't play ball. They could have very easily decided that the eligibility matters at allocation time, and simply continued to allow pre-existing holders to use their domains. Or they could have steadily increased the prices to ease people out on their own pace. Or many other things. Instead they yank all of them simultaneously with no recourse: the worst possible outcome for everyone.
Honestly though, I wonder what people who registered .eu domains were thinking. There's no real benefit to having one and the true nature of the EU Commission is not really a secret, albeit it's not covered by American media. If you willingly submit yourself to the Commission when you don't have to, you're almost signing up for some kind of abuse.