The below explains the EU’s equal protection for these things. Makes sense to me:
An EU country cannot offer free admission to cultural sites or public
services (like universities) solely to its own citizens while charging
citizens of other EU countries.
Under EU law, discrimination on the grounds of nationality is strictly
prohibited within the scope of the EU Treaties, particularly
concerning the free movement of persons and services. The core
principle is that all EU citizens must be treated the same as the host
country's nationals in a situation governed by EU law.
Key implications of this principle:
Equal Treatment: If a public museum, art gallery, or university in one
EU country offers free admission or tuition to its own citizens, it
must extend the same free access to all other EU citizens under the
same conditions.
Access to Services: The freedom to provide and receive services
(including tourism and education) means that recipients of those
services must be able to enjoy them under the same conditions as
nationals.
Non-EU Citizens: This rule of equal treatment applies to EU citizens.
Non-EU citizens (sometimes referred to as third-country nationals) can
generally be charged different fees or be subject to different
conditions, although some countries may choose to offer them free
access as well (e.g., Germany offering free university tuition to all
international students at one time).
A landmark European Court of Justice (CJEU) case confirmed that
differential pricing for state-owned museums based purely on
nationality is illegal for EU citizens.
Happy travels!