Isn't that because a lot of their vaccines get shipped all over the world? We need doses for ~7B people in total. I don't see anything there that says they're planning on administering multiple vaccination rounds per person.
The real reason the EU needs this kind of capacity is that the current EU vaccination campaign is going very poorly. Most of the population will only get vaccinated late in summer and autumn, so the yearly capacity needs to be appropriate to at least get it done this year and before the next flu season.
Oh, and the EU produces vaccines for a lot of others like UK, Israel and the US, as well as most third-world-countries. Imports into the EU are neglegible.
There’s a world of nearly eight billion people to vaccinate out there, and the manufacturing capacity may be useful when we start playing with mRNA vaccines for things like malaria.
Hint 2:
""Quite often vaccines are more effective than natural immunity but we might need to vaccinate everybody every year, or two or three, for quite some time and maybe forever."
https://www.reuters.com/article/us-health-coronavirus-eu-vac...
"The European Union aims to increase the region’s COVID-19 vaccine production capacity to 2-3 billion doses per year by the end of 2021"
Hint: The EU has about 400 Million people