Note that the 2 main arguments and counter arguments: it helps protect people's information vs it increases the barrier of entry are NOT exclusive. Both can be valid at the same time and I believe that in many regulations they are both valid. That's how life works, a chain of compromises.
So yes, taking on new and unknown (to the creator) legal liability from some regulation is a great reason to shut down a side project.
If you have time/money or plan to make money, GDPR compliance isn't terribly difficult. But free/cash-strapped service providers would probably think twice before becoming compliant (which is why a lot of local US news websites just don't allow European visitors -- compliance is somewhat expensive, and local news in the US isn't doing too great right now).
[1] https://developers.trello.com/docs/personal-data-storage
Many companies will attempt to follow the rules, even if they think that the probability of getting fined is low.