It's not about protesting, it's about representation. They were born into what are now, Germany, Germany, Italy, USA, Germany, Polish.
Why not any of the below ?
Austria: Wolfgang Amadeus Mozart
Belgium: Georges Lemaître
Bulgaria: Saint Cyril
Croatia: Nikola Tesla
Cyprus: Zeno of Citium
Czechia: Franz Kafka
Denmark: Hans Christian Andersen
Estonia: Jaan Kross
Finland: Jean Sibelius
France: Napoleon Bonaparte
Greece: Aristotle
Hungary: Franz Liszt
Ireland: James Joyce
Latvia: Mark Rothko
Lithuania: Mikalojus Konstantinas Čiurlionis
Luxembourg: Robert Schuman
Malta: Jean de Valette
Netherlands: Rembrandt van Rijn
Portugal: Vasco da Gama
Romania: Nadia Comăneci
Slovakia: Andy Warhol
Slovenia: Slavoj Žižek
Spain: Pablo Picasso
Sweden: Alfred Nobel
Why was Callas chosen over Joyce ? why was Beethovan chosen over Mozart ?
Beethoven in particular is easy. The EU doesn't have a national anthem, or a national flag, because it insists it isn't a nation, but Europe does have an anthem and a flag and of course the EU represents Europe, so it uses those, that's Europe's flag on the money. Europe's anthem is basically the bit you know from Beethoven's Ninth Symphony.
Officially the EU prefers Karajan's arrangement, if you're a huge classical music fan you'll recognise this immediately, but for most people it's just obviously the Ninth.
Marcus Rotkowitz was Jewish, born in Dvinsk, Russian Empire (today Daugavpils in Latvia) and emigrated when he was 10 (and Latvia wasn't a country yet.) At home, he spoke Yiddish and Russian, and probably didn't know a word in Latvian (at the time, Dvinsk population was half Jewish, with the rest divided between Russians, Poles, and Latvians).
Your idea that he's the guy who should represent Latvia on a European banknote would probably quickly get you burned at the stake at Doms Square in Riga.
Of course not, but people may complain that none of them are from their country. Maybe someone from Spain would like to see Picasso or some other famous Spanish figure in there. That's the reason for using generic images, the EU and the Eurozone in particular is a trade alliance of countries with different cultures.
I like what they did with coins the best, where one face is common, showing a map of Europe, and the other is free for the issuing country to choose from. I like the message it delivers, different cultures, united. And as people travel, they will bring coins from their countries, the resulting effect is that if you go to a Eurozone country, you are likely to see coins in circulation from all over Europe, which is a concrete example of free trade happening.
I wish they did the same for banknotes: one side generic, one side country-specific, but it may be impractical.
The reason not to do this with banknotes is that they wouldn't be accepted. "No weird money".
I happen to live in a city on England's south coast. So Scotland is quite far away and understandably Scottish banknotes, though legally equivalent to the notes you'd get here in most senses, are rarely seen. I know what they're supposed to look like and that they're 1:1 equivalent, but of course the guy who runs the Chinese takeaway near me wouldn't have seen one before. So what happens when a Glaswegian down for the weekend wants to order some food and tries to pay with the Scottish £10 in his wallet? The owner doesn't accept it. "No, no, no!". The Glaswegian insists it's legal tender [which is irrelevant, but if you don't know why it's irrelevant feel free to go look it up, it's not helpful for me to tell him this even if he believes me and I see no reason I need to explain to you either] and of course all the time they're arguing about money I am not getting my food.
So I took the man's Scottish £10 and handed the restaurant owner an English £10 because I don't care and now I can order food. Weird money is bad.
If you live in a border town you'd see notes from both sides. If you work in a tourist-facing industry you might recognise most of the variants because tourists tend to have their country's notes. But if you're some small town shopkeeper in Poland why would you know that this is real €200 note from Luxemboug? It's probably a fake, isn't it? So you make friction for these notes higher (some shopkeepers won't accept them) and even if legally they're fine you can't fix that friction in practice so people hate this outcome.
It's not a matter of protesting (nor is it a matter of nationalism).
It's a matter of bureocrats remembering that there are more countries in the eurozone than banknotes, and even if that wasn't the case, their denominations can be read as hierarchy.
Why not any of the below ?
Austria: Wolfgang Amadeus Mozart Belgium: Georges Lemaître Bulgaria: Saint Cyril Croatia: Nikola Tesla Cyprus: Zeno of Citium Czechia: Franz Kafka Denmark: Hans Christian Andersen Estonia: Jaan Kross Finland: Jean Sibelius France: Napoleon Bonaparte Greece: Aristotle Hungary: Franz Liszt Ireland: James Joyce Latvia: Mark Rothko Lithuania: Mikalojus Konstantinas Čiurlionis Luxembourg: Robert Schuman Malta: Jean de Valette Netherlands: Rembrandt van Rijn Portugal: Vasco da Gama Romania: Nadia Comăneci Slovakia: Andy Warhol Slovenia: Slavoj Žižek Spain: Pablo Picasso Sweden: Alfred Nobel
Why was Callas chosen over Joyce ? why was Beethovan chosen over Mozart ?