What is the ruling on temporary marriage (mut'ah) for someone who is unable to marry in this era, and why was it forbidden after being permissible in the early days of Islam?

The needs of youth and the intensity of immorality do not justify committing what Allah has forbidden, such as the prohibited mut'ah (temporary) marriage. Allah has legislated legitimate marriage as an alternative for those who are able, and He has promised His assistance. For those who are unable to marry, they must be patient and chaste, and take supportive measures such as fasting, in accordance with the Almighty's saying: (And let those who find not [the means for] marriage abstain [from sexual relations] until Allah enriches them from His bounty). The prohibition of mut'ah after it was initially permissible in early Islam came gradually, to ease the transition for people from the customs of the pre-Islamic era (Jahiliyyah).