* There's no existing infrastructure. OVH and Hetzner are great for smaller projects and businesses, but no serious enterprises and governments are using them, as far as I know. There's no real alternatives to Android, iOS and Windows. (Sorry, folks; not the year of the Linux desktop quite yet.)
* It's expensive and time-consuming. The on-prem to cloud migration took decades for most (and is still ongoing for many!); even if a viable alternative existed right now, migrating from AWS to a domestic cloud service is a 5+ year project that distracts from other initiatives.
* Compounding on the above, business leaders still largely expect this to be a one-time event, believing there's low likelihood this policy would last past 2028. You're not going to see much beyond research and planning for at least 4 years, before anyone commits to investing hundreds of millions in a massive tech migration.
* Besides all that, where do you actually move to, specifically? You can say "the EU," but given the rise of populism in the region, are you confident enough to bet $500m that there won't be a "Gexit", "Frexit" or "Swexit"? Is every country in the EU going to make their own Amazon-scale cloud provider and Windows-scale operating system? Seems unrealistic.
The most realistic outcome is that MS, Meta, and Alphabet all continue to push region-specific data residency for their cloud platforms and OS'es, so customers are more insulated against foreign policy changes... and charge European customers more for the trouble.