I've been playing this game for almost 10 years. I originally played on PC-NA, then moved to PC-EU, but I return to NA from time to time (several times a week). Having to buy the same stuff on every server is dissatisfactory to say the least
Historically ZOS has some inconsistency in terms of in-game purchases. Some items exist as both an account upgrade and a Crown Store purchase. If you buy something in crown store, it will only work on the server where purchase was made.
For example, years ago I got my hands on a Any Race, Any Alliance upgrade code and I enjoy the benefits on both servers to this day, but I had to purchase Imperial Upgrade on both servers.
Want to put mundus in your house? Be a good lad and spend crowns on both servers. Like the assistant banker/dealer? Crown Store is open 24/7. Want to put a tiny Auri-El statue in your house on EU that was free for ESO+ subscribers and you have it on NA? Too bad you didn't play it back when it was in the Crown Store.
Things that are purchased in the Crown Store and that get into the Collections UI should be made available account-wide, on both servers. It won't change anything for those who only play on one server, but it will make life better for those players who actively play on both servers.