Is it because Japanese pronunciation is easier to pick up than Mandarin? Also, is there a such thing as “Chinese” anime (as in made in China / Taiwan being originally in Mandarin), they do have an equvalent of Manga known as Manhua (漫畫) but is it even popular to the same extent as the Japanese counterparts? Why do those types of foreigners favor Japanese (language) over Mandarin regarding pronunciation?
Are sentences in Japanese easier to pronounce in comparison to Mandarin? JP does not have tones (rather pitch accent) with an “alphabet” of some sort (known as ひらがな & カタカナ) even though they have 漢字 (Furigana is used for placing kana above Kanji for native speakers to understand) while Mandarin places a big emphasis on tones and its entirelty written in 漢字 (for transliteration, either Pinyin or Bopomofo is used).
It’s pretty much entirely because anime (and adjacent content). You can’t exclude that and expect a coherent answer.
People learn languages when they have a cultural reason to do so – such as engaging with media in that language or wanting to interact with people who speak it (for business/relationships/diplomacy/whatever).
Hollywood movies and rock-and-roll were big drivers that pushed people to learn English last century. Programming and the internet probably pushed a bunch of people to learn it in the last ~20 years. K-Pop and K-Drama have been drivers for learning Korean recently. German was one of the major languages (along with French) for math and science before WWI – but was overtaken by English after that. You get the picture, I hope.
If the US continues on its current path, maybe in a few decades all the new research papers coming out will be in Chinese instead and everyone will learn Mandarin to discuss new tech. 🤷️
The thing with English is it’s now the international language, it’s pretty much every country’s chosen second language. While Mandarin is still only in one country.