What’s the reason why females should not wear the tzitzit tallit, as opposed to other mitzvot which they aren’t obligated but can fulfill? We be very happy if source of answer can be shared. Thank you!

Because they are not obligated in all of the 613 mitzvot which the tzitzit represent (Bamidbar 15, 39), and even men aren't obligated m'd'Oraita to wear a 4 cornered garment to bring upon themselves this obligation, so when a woman does so, it looks like religious arrogance and is prohibited (Maharil, New Resp. 7, and Customs of Tzitzit 4, brought by Beit Yosef and Rama, Or.Ch. 17, 2). The Aruch HaShulchan (17, 3) cites them and also adds that fulfilling this mitzva when exempted seems especially arrogant because it is a constant full-time mitzva all year round, as opposed to women taking a lulav or shofar which is short and temporary. In addition, the Targum Yonatan of the pasuk "the clothing of a man shall not be on a woman" (Dvarim 22, 5), explains that it's referring to tzitzit and tefilin, and is cited as halacha by the Levush (17, 2), Ben Ish Chai (Lech L'cha 13) and R. Moshe Feinstein (Igrot Moshe 4, 49), who also adds that it's prohibited to change traditions, and especially prohibited when done as part of a feminist agenda, which is clearly often the case. The Maharil, ibid, adds there that it's an additional problem to wear on Shabbat where there is no eruv, for women aren't obligated and it's not considered "wearing" for them, but rather "carrying".