What is the wisdom behind a woman uncovering her face and hands during Umrah and Hajj, and why do some women not adhere to this?

It is not obligatory for a woman in ihram to uncover her face and hands. Rather, it is forbidden for her to wear the niqab and gloves, based on the Prophet's (peace be upon him) saying: "A woman in ihram should not wear the niqab nor gloves." It is permissible for a woman in ihram to cover her face and hands when necessary, such as by lowering her khimar over her face or covering her hands with her garment. Indeed, this becomes obligatory when she mixes with non-mahram men, and no fidyah is required of her for this, according to the hadith of Aisha (may Allah be pleased with her). The wisdom behind forbidding the wearing of the niqab and gloves is an act of devotion to Allah, and this ruling is general for all Muslim women.