A well-known gemara in the Yerushalmi (Rosh Hashanah 6a) says:
"רשב"ל אמר אף שמות המלאכים עלו בידן מבבל. בראשונה (ישעיהו ו׳:ו׳) ויעף אלי אחד מן השרפים (שם) שרפים עומדים ממעל לו מיכן והילך (דנייאל ט) והאיש גבריאל (דנייאל י) כי אם מיכאל שרכם."
Translation: "Rabbi Shimon ben Lakish said: Also the names of the angels came with from Babylon. In the beginning (Yesha'ayhu 6:6) "Then one of the seraphs flew over to me" (ibid.) "Seraphs stood in attendance on Him" from here on (Daniel 9) "and the man Gavriel" (Daniel 10) "except your prince, Michael"."
What's the reason that the names of the angels had to brought back with them? Were the names created there?