Or it costs time and resources to meet EU regulations and they launched in other marketplaces first while they work on complying, and verifying their compliance with the laws?
This isn't uncommon for new products, and there doesn't need to be a conspiracy theory.
Or maybe they know that their plans to connect to the fediverse will leave them with tons of personal data they wouldn't be allowed to collect under GDPR. Although that doesn't matter since the EU is considering any company worldwide to be subject to GDPR when they collect data from EU residents.
1. They know that Threads is doing things which are not acceptable by EU rules.
2. They want to fight the EU so that EU makes rules that allow Meta to disregard the privacy of their users.