Translating from German:

It is almost superfluous to mention single points as evidence for the "unhistoric" character of the book. The exegetes have often emphasized how unthinkable a feast that all dignitaries of the Persian court participate in (1:1-4), how absurd a royal decree to all men to maintain the final say in their household (1:22), and how unlikely the promulgation of decrees in all languages of the world empire rather than in the official Aramaic (3:12; 8:9) would be. To these observations is usually added that neither a Vashti nor an Esther were ever queens in the Persian empire, that the only historically verifiable character of the book, Ahasveros or Xerxes I, had a queen by the name of Amestris and that as members of the royal harem neither Esther nor Vashti could have been called 'queen'. Additionally the Persian kings were obliged to choose their queen from one of the seven noble families. Therefore Esther doesn't even come into consideration. A Jew as vizier at the Persian court (8:2; 10:3) is extremely unlikely and a Persian king who sanctions a civil war within his own empire (8:8; 9:11 sq.) entirely unthinkable. Finally, if Mordechai had been one of the exiles who were deported from Jerusalem 597 BC, then he would have been more than 120 years old in the 12th year of Xerxes' reign (3:7) and his cousin Esther would not have been the beautiful young girl who won over the king to elevate her to queen (2:17).

J.A. Loader, "Das Buch Ester", in: Kaiser/Loader/Müller, "Das Hohelied, Klagelieder, Das Buch Ester" (Das Alte Testament Deutsch 16/2), Göttingen 1992, p. 208.

The book is extant in three version (Masoretic text, Septuagint version, Alpha text (shorter Greek version) the exact genetic relationship of which is unclear. In any case the book contains typical structural elements of a Hellenistic novel and is probably to be dated into the 3rd century BC (regardless of whether the Hebrew or the Greek text versions are the earlier ones), the Persian 5th century setting is just that - a setting.

Not sure what you are asking for with "How did it get included in the Bible": it is included in the Septuagint, so the default assumption is that you will find it in the Orthodox bible (full Septuagint canon) as well as in the Catholic one (Septuagint canon minus the Prayer of Manasseh, 1 Esdras, 3 Maccabees and Psalm 151). A Hebrew version is also extant, therefore it wasn't thrown out based on veritas Hebraica grounds by the Protestants.